394 MEMOIKS OF THE NATIONAL ACADEMY OF SCIENCES. 



while the ovariau lobe is yet ci'owded with ripe ova ready to be laid, on the ovariau wall uext 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 follicular tissue (F. E.), but eventually each egg has a covering of its own. Between very 

 young ova (e) no larger than the epithelial cell, and the maturer egg (e'j 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 zoi'al stage, and the egg 

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

 is a zoi-a like form. The materials for the yolk must be derive<l 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 [Homartis) and 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. H, 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,' to the left) which is ^^^ iw^'l^ 

 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 uncleoli. The older eggs are spherical ; their food yolk is often vacuolated, as in 

 later stages, and they are invested by a single mend)rane, 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 uext the middle line, where, as already stated, the young ova first make their appearance. 

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

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

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

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

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

 ovarian egg of 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 Ilomarus. 



(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 olivp 

 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 protophxsm, 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. 3, 6. 

 Fig. G 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. 6, and the 

 oldest eggs lie at the periphery. The germogeus, the centers of dis])ersion 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 indiftercut nuclei of the ovarian stroma to the 

 large peripheral ova. The ovary is supjilied with blood by means of sinuses which i)enetrate to 

 all its parts (Bl. 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^} swells out, becomes sx)herical, and its chromatin has the charac- 



