THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. IX. AUGUST, 1888. No. 8. 



Elementary histological studies of the Cray-flsh.— X. 



By henry L. OSBORN. 



CHAPTER IV. THE OVARY. 



We have now examined, in this series of elementary studies of animal tis- 

 sues, the liver and the intestine of the cray-fish. This course of the essen- 

 tials, if fully understood, may be used as an introduction to further studies 

 of histology, so far as it is pursued, by means of sections. It seems, how- 

 ever, desirable, and has been from the first a part of mv purpose in connec- 

 tion w^ith the present series, to make elementary studies of most of the parts 

 of the body of the cray-fish, completing the round of almost all the various 

 organs in the entire anatomy. The usual course of anatomical or physiolog- 

 ical study would suggest treating the reproductive system last. To do this, 

 however, is not convenient in the present instance ; and the order being of 

 no great importance for the general purpose of my work, I shall depart from 

 it and proceed at once to the examination of the ovary and testes, leaving 

 muscle and nerve, the sense organs and the skin until some later time. 



I. Preparation of the section, — In selecting the specimen from which 

 to obtain material for studying the ovary it is necessarv to bear in mind that 

 the sexes are separate in these animals, and to learn how to distinguish the 

 males from the females. The shape of the body and the coloring are alike 

 in both sexes, and are hence of no assistance for this purpose. At first sight 

 the observer would imagine the two sexes were not distinguishable, but care- 

 ful examination of the 'legs' of the abdomen of several specimens will show 

 him that in some those borne on the front rings of the abdomen next the trunk 

 are much larger than they are in others. He can sort all his specimens into 

 two groups, in one group of which he places those whose front abdominal 

 legs are like in shape and size to those behind, while in the other he places 

 those whose front legs differ in both shape and size. The former are females, 

 the latter are males. The enlarged legs are used in the act of copulation to 

 guide the spermatic fluid to the female oviduct. Besides these conspicuous 

 difi'erences between the male and the female there is also a dift'erence in the 

 situation of the opening of the reproductive organs. In the females these are 

 on the basal joint of the thoracic leg, third from the last on each side, while 

 in the male the}' are on the basal joint of the last thoracic leg on each side. 



EXPLANATION OF THE PLATE. 



Fig. I. — General view of ovary with eggs. c. Space between egg and wall of follicle. 



Fig. 2. — Enlarged view of wall of follicle at point d. d. Wall of follicle. 



Fig. 3. — Surface view of follicle wall. e. Iruinature egg in position in ovary. 



Fig. 4 — Enlarged view of centre of one egg. _/". Yolk globules enlarged. 



Fig. 5. — Immature egg. g. Protoplnsm of mature egg. 



a. Nucleus of mature egg. h. Nucleus or germinal vesicle of mature egg, 



b. Yolk globules. 



