394 MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 







while the ovarian lobe is yet crowded with ripe ova ready to be laid, on the ovarian wall next the 

 middle line of the body. The process seems to be as follows : The nuclei of the cells of the ger- 

 minal epithelium increase in size along a certain tract. The cells grow rapidly and are slowly 

 dehisced or pressed into the cavity of the sac. Each is surrounded by a coat of follicle cells. 

 This is formed by the ingrowth of the germinal epithelium about the egg. Sometimes .several 

 ova occupy a common pouch (Ger.) which is separated from the rest of the ovary by sheets 

 of follicnlar tissue (F. E.), but eventually each egg has a covering of its own. Between very 

 young ova (e) no larger than the epithelial cell, aud the maturer egg (e l ) every stage can be 

 traced. The yolk appears very early as a fine granular deposit in the protoplasm of the cell. 



In this species the development is nearly direct, there being no zoeal stage, and the egg 

 contains more than nine times as much yolk as the egg of Alphcun minus, in which the first larva 

 is a zoea-liko form. The materials for the yolk must be derived directly from the blood, and in this 

 form the germinal epithelium is bathed with the blood current. Where there is an enormous food 

 yolk blood must be supplied to the developing ova in more than the usual quantity. This is often 

 accomplished by reentrant blood sinuses which penetrate all parts of the ovarian stroma, as in 

 the lobster (Homariia) aud in the cephalopods, which are .precocious in development and conse- 

 quently deposit a great store of yolk in the egg. In the latter the follicular epithelium is folded 

 in a remarkable manner about the egg to increase its nutritive surface. 



The germinal vesicle (Fig. 11, G. V.) is filled with coarse chromatin grains, and in the early 

 phases grows relatively faster than the rest of the egg. In the egg, (e, 1 to the left) which is ^ s inch 

 in diameter, the diameter of the germinal vesicle is one-half that of the entire egg. The chromatin 

 grains increase in size until there are formed, as in an egg like the last, six or more large masses 

 of chromatin, or uucleoli. The older eggs are spherical ; their food yolk is often vacuolated, as in 

 later stages, and they are invested by a single membrane, the chorion, which is a chitenous secre- 

 tion of the follicular cells. 



In the ripe ovary of this Alpheus the mature eggs fill the ovarian sac, except at the lower 

 portion next the middle line, where, as already stated, the young ova first make their appearance. 

 These mature eggs are closely crowded aud irregular in shape, and their bulk greatly distends the 

 body of the prawn. The choriou is now fully formed and closely invests the vitellus. The yolk 

 is in the form of spherules, usually fused aud always vacuolated in preparations which have been 

 subjected to alcohol aud turpentine. In the ripe egg the nucleus was not seen, but it is quite 

 probable that careful sectioning would show that it lay at the surface, as is th case with the ripe 

 ovarian egg ef the lobster, which is often left in the ovary, after the bulk of the eggs are laid. 

 We thus conclude that the extrusion of polar cells may be internal, that is, may take place within 

 the ovary, as is sometimes, if not always, the case with Homurux. 



(b) The*Lobster (Homarus americanus). The ovaries of the lobster consist of two lobes or rods 

 of tissue, united by a short transverse bar. When filled with eggs their color is a dark olive 

 green, except in young females, where the color of the immature ovary is variable. Each lobe is 

 composed of an outer wall, which is a felt of muscle and connective tissue fibers with very small 

 nuclei, and of a loose framework of germinal epithelium, which penetrates all parts of the lobe. 

 The latter is a syncytium and consists of a matrix in which great numbers of small nuclei are 

 embedded. These nuclei, with surrounding protoplasm, give rise (1) to ova and (2) to cells of the 

 egg follicle. 



The growth of the ovarian egg from the epithelial nucleus is illustrated in PI. xxv, Figs. ,'5, 0. 

 Fig. 6 is from a section through the posterior end of an ovarian lobe of a lobster obtained from the 

 Baltimore markets in January. Fig. 3 shows the central portion of this section greatly enlarged 

 The diameter of the entire section is about twice that of the part represented in Fig. 0, and the 

 oldest eggs lie at the periphery. The germogens, the centers of dispersion of new eggs, lie nearly 

 in the long axis of the lobe. We can therefore trace in a single good section at this stage the de- 

 velopment of the egg through every stage, from the indifferent nuclei of the ovarian stroma to the 

 large peripheral ova. The ovary is supplied with blood by means of sinuses which penetrate to 

 all its parts (IJ1. S.). The sinuses are definite reentrant channels with thin membranous walls. 



The ovarian tissue (Ct. S.) consists of a fibrous matrix in which numerous oval granular nuclei 

 are embedded. The process of the conversion of the epithelial cells into eggs is shown in Fig. 3. 

 The epithelial nucleus (O, O a ) swells out, becomes spherical, and its chromatiu has the charac- 



