毛皮獣の被毛の研究，特にNutriaの被毛について

A study on the pelage of the nutria referring to the pelage-change of fur animals in general

Otaishi Satoru

広島大学水畜産学部紀要

Journal of the Faculty of Fisheries and Animal Husbandry, Hiroshima University

1) In the three months old foetus of the nutria, the development of the lanugo hair anlage are almost completed, and the dorsal original trio group are growing to be "Scheiden haare".
The hair anlage developes in the order of caput, dorsum, abdomen and pectus and so the anlage on the pectus is still in hair germ stage being devoid of pigment. Therefore three months foetus is of a dark gray nude figure.
2) At birth a baby animal is covered with lanugo hairs. In about a half number of lanugo hair follicles contained in the hair groups the large-type hairs are growing to about one-fourth of the whole length and the small-type hairs to about a half of the length.
At several hours after birth, they may be served as keeping the body heat in the cold water.
At birth original trio group are still young or the younger hairs and most of the sublateral hairs are in hair germ state "Scheiden haare".
There is no sign of the postnatal sublateral hair growth.
3) During about a month after birth, the lanugo hair groups accomplish their development and most of the lanugo hairs become club hairs while the rest of them remain as young hairs.
A small number of club hairs are accompanied with their successors.
The development of new postnatal sublateral hair follicle occurs rarely.
4) The lanugo hair group is composed of original trio group and sublateral hairs are arranged on both sides of trio group. The largest lanugo hair group has fifteen follicles and the smallest group three of them.
Generally, lanugo hair groups are of "Fifteen hairs type", "Seven hairs type", "Three hairs type", or middle number type.
5) The development of new postnatal sublateral hair follicle is most active at about two months after birth. It is evident that the additional development of new hair follicles is continued until eight month old and ceased before twelve months.
6) The pseudo hair bundle is made of several post sublateral hair follicles concentrating around a lanugo cross-hair follicle or a lanugo under hair follicle. In this occasion the original trio group contained in the large hair group, fifteen lanugo hair type group, are composed of a first over hair and two second over hairs, follicles of which are almost independent from pseudo hair bundles.
In the hair group of the seven lanugo hair type, the group is composed of six pseudo hair bundles and a solitary central hair follicle. In the hair group of the three lanugo hair type, the group is composed of three pseudo hair bundles concentrating around original trio hair follicles.
In such a way above mentioned, every large over hair follicle gives rise to a solitary hair, and then a generation of coupled hair bundle, or rarely a generation of trib hair bundle. Other small over hair follicle, cross hair follicle, or under hair follicle passes a solitary hair and the generation of true bundle occurs like the large over hair follicles. These solitary hairs and true bundles are combined together to make several pseudo hair bundles.
The hair groups of the adult pelage are composed of the above mentioned hair bundles which are about the same number as the follicles of lanugo hair groups.
The hair group density of the adult pelage is only about four percent of the juvenal pelage, but the hair density of the adult is about a half of the juvenal pelage.
7) It seems highly probable that the development of all follicles is not brought about by the process of proliferation, but develops and migrates down from the stratum germinativum.
8) The epitherial tissues enclosing the tip of the successor extend upward to about the level of the sebaceous gland, and along the epitherial tissue on the outside of the capsule in which the hair club is buried.
The level of the sebacenus glands is just at the base of the hair canal through which the tip of the young hair appeares on the surface of the body. The successors of large over hairs extend upward looking like to be carried on the back of the club hairs and to protect the predecessors.
9) So far as the animal is healthy the development of the successors are repeated periodically despite the outside temperature.
10) Both over and under hair are always enlarged in size to some degree by every replacement during the growth period of the animal. The under hair of the adult pelage showes no particular change in type in their generation. There is neither seasonal nor sexual change. However, it is apparent that dorsal under hairs are larger than abdominal under hairs in size.
11) There is no seasonal difference in large type over hairs. This comes from the fact that they are remained in the skin from the time of hair germs untill the shedding of club hairs covering about 4.5-5.0 months. Small type over hairs and under hairs the period of retention in the warm season is about 3.5-4.0 months being shorter than that of large over hairs, while the retention in the cool season lasts about 5.5-6.0 months being longer than that of the large over hairs.
12) After twel_ve months old, there is no increase of new hair follicle in number in the stratum germinativum.
On account of the retention of club hairs and the participation of successors, the hair follicles produce the generation of true hair bundles, namely coulpied hairs bundles and trio hairs bundles and these true hair bundles make pseudo hair bundles.
In the cold season, the largest number of hairs which are contained in the generation of true hair bundle developping from the same follicle is three. This is the trio hairs bundle.
There is no case in which all hairs of the trio hairs bundle are club hairs, i. e. T GnO, G 1+10, G,+20. All hairs of the trio hair bundles are composed of two club hairs and a growing hair, i.e. TG,Q, G,+IO, Gn+2Y or TG"O, Gn+IO, Gn+2C.
In the warm season there is no trio hairs bundle in the generation of hair bundles. They are coupled hairs bundles or solitary hair follicles. The coupled hairs are not of two club hairs, i. e. PG,O, Gn+JO.
Accordingly the density of the hair in the cool season is about twice as much as that of the warm season.
13) The medulla of the under hair is of the chain shape and is composed of alternately arranged air chambers and medulla elements. The medulla in which the cells are arranged in a continuous line, has air chambers enclosed with medulla elements respectively. These air chambers are formerly occupied by the karyoplasm. Therefore every air chamber is formed in each cell.
14) In the over hair, the medulla fragments fix firmly on the innerwall of the cortex pipe at about regular intervals, and the microscopical observation of the longitudinal section reveals that they are confront, crossed each other or in net-like shape, forming zigzag air hollow in the medulla.
15) In the under hair stalk, there are many granular pigments in the medulla elements which are found between air chambers, while in the over hair stalk, the pigments are scattered uniformly in the cortex and the medulla.
16) The keratinization of the cytoplasm of hair cuticular cells may occur earlier than that of the cortex and the medulla. However, the keratinization of the cortex may occur simultaneously with the medulla.
17) The crimps of the under hair seems to be brought about by the cuticular cells which prevent cortex cells from the uniform arrangement in the peak of the hair bulb during the growth of the hair. Either in dorsal or in abdominal hair cover, the stalk of the under hair which has regular crimps is about thirteen micra in diameter, and the stalk of the under hair which is entirely surrounded with single cuticular coronal scales is about twenty micra in maximum. The blade of the under hair which has *"jomon" type coronal scales is about twenty-five micra in diameter in maximum. * "jomon" = Cord marked
18) When the hair cuticular scales are consisted of single cuticular coronal scales, the medulla cells are arranged in a line.
19) The observation on the cross-1>ections of the hair stalk indicates the change of the singular cell to the pulural in the cuticle, the medulla-and the cortex-cell respectively. From this the boundary shifting from the under hair to over hair is considered very probable.
20) The hairs of the nutria are classified as follow
(omission)
1) The first over hairs are the longest having no hair constriction. As a rule the hair blade is dark brown in color without agouti bands. There are some exceptions that have sub-apical light yellow bands.
2) The second over hairs are the next in length. The hair blade is wide with bright yellow agouti bands in the mid-blade. In the middle of the hair shaft there is a narrow constriction. In many of them the hair stalk is larger in diameter than that of the first over hair stalk.
3) cross-hairs,
It is possible to classify cross-hairs into two, i. e. over hairs and under hairs. The size of the stalk of the cross-over hair is the same as that of the cross-under hair. The hair blade of the cross-over hair is somewhat wider than that of the crossunder hair in diameter and the former has an agouti band while the latter is a blade with dark shade. The cross-under hair belongs to a large type under hair, and the features
of hair bla:le, hair coastriction and hair stalk are very much similar to those of the under hair. The width of the cross-hair stalk is intermediate between that of the under hair and that of the over hair and the name "cross-hair zone" should be applicable.
4) under hairs,
The under hairs being without the cross-hair zone are simply ordinary under hairs.
21) There is no development of new hair follicle after twelve months old in the nutria. At the several months after the birth, the density of the hair groups is decreased remarkably, but the density of the adult pelage is kept by about a half of that of juvenal pelage in degree on account of the development of postnatal sublateral hair follicles. However, at this time the density of the pelage is highest in the
life of the nutria being provided with the fine under hair.
The density of the ab:lominal pelage is higher than the dorsal pelage and the quality of the hair in the former is finer than in the latter, so the skin for the fur cut along the mid-dorsal line should be prized. The ab:lominal skin of the juvenal animal is thin and brittle. From this reason the nutrias of above twelve months after birth and above four-five Kgs have utility value for the fur.
In many kinds of ro:lents there are normally two seasonal molts in a year, i. e. spring and autumn, and they supply us with fresh and fine winter pelages duringonly about two months after December, while in the nutria there is continuous replacement of hairs throughout a year. However in the cool season the shedding of the club hair is delayed, increasing the density of the pelage above twice as much
as the warm season.
Such prolonged retention occurs not only in winter, but also in late spring.
From the reason above mentioned we can understand that if this animal is kept in the pen supplied with fresh and cool water, and carefully treated, the superior pelts of higher value is maintained for considerably long period in a year.
22) The findings so far obtained in the present investigation are as follows:
1) The arrangement of hair follicles in the hair groups has been made clear.
2) The air chamber of the under hair is formed in the medulla cell in theplace which is occupied by the nucleus.
3) The occurrence of the crimps in the wool of the sheep is said to be brought about by some chemical procedure but the crimps of the under hair in the nutria is resulted from the change of arrangement of cells.
4) Speaking morpho-genetically, the shifting of the under hair to the over hair is the shifting of singular cell to multiple cells.
5) There is no sexual age or seasonal difference in the under hair of the adult nutria.
6) There is no change in generation of hairs of the nutria according to the season, but during the cool season there occurrs very rare shedding of the hair. In the warm season 1-2 hairs are retained in a follicle while in the cool season 2-3 hairs are held.
7) In the most of the fur bearing animals there are regulary 2 shedding periods, spring and autumn in a year and so the pelting time is limited. However, the nutria replaces the fur all around the year. Accordingly we can control the pelting season by managing environmental condition artificially.

Zoology [ 480 ]

jpn

広島大学水畜産学部

[ISSN] 0440-8756

[NCID] AN00213563