MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 395 



teristic granular appearance of the germinal vesicle of the young egg. The iirst trace of (he yolk 

 (O :! , O 4 , O 5 ) appears in the outer granular layer which surrounds the germinal vesicle. This layer 

 represents primarily the cell protoplasm, in which the yolk is formed. The cell takes on a definite 

 shape and is very early invested with a follicular coat (F. C.). In an egg a little older (O 7 ) the 

 nucleolus has appeared, and in still older eggs (Fig. 6, O, O 1 ) a delicate choriou (Ch.) can be 

 seen. This is secreted by the cells of the follicular envelope (F. C.). The growing eggs pass out 

 from the central to the peripheral parts of the lobe in the sheets of stroma between the blood 

 sinuses. Distinct yolk spherules are very early seen (O 7 ) and are of uniform size, but in maturer 

 eggs (Fig. 6, O, O 1 ) the germinal vesicle is sometimes surrounded by a central layer of small 

 spherules and a peripheral layer of larger ones. The germinal vesicle is centrally situated and 

 always contains a single excentric uucleolns, besides stellate masses in the chromatin reticnlum.* 

 (c) The Spiny Lobster (Palinurus). In the spiny or rock lobster from the Bahamas the ova 

 originate exactly as in Elomarus, and the structure of the ovary is essentially the same. There 

 are several uucleoli, as in Alpheus. The ovary is not nearly so richly supplied with blood sinnses 

 as in the cases just considered. This is perhaps correlated with the fact that the amount of yolk 



* Since the above accouut was written I have been able to study the structure of the ovary more thoroughly, 

 and the subjoined notes are largely extracted from a preliminary notice on "The Reproductive Organs and Early 

 Stages of Development of the American Lobster." (23.) 



The structure of the mature ovary is somewhat peculiar. The free, nnextruded eggs till the lumen of tin- 

 ovarian lobes. The lobe or tube itself consists of the proper ovarian tissue and the outer muscular wall, which is 

 very thick. The stroma is characterized by the presence of gland-like structures, blood sinuses, and immature ova. 

 The glands are in close relation with the growing eggs. They are plaited or folded structures, and consist of a single 

 layer of columuar cells, the boundaries of which are iudistiuct. The lumen of the fold usually contains a granular 

 residue, but often yolk and degenerating nuclei. It seems possible that these structures are comparable to yullc 

 (/lands, and that their function is to supply the growing ova at this stage with a part of their massive fond yolk. 

 Three days after the extrusion of the eggs tho glandular c;eea have much thicker walls; the rapidly dividing cells 

 are smaller, and their nuclei lie at various levels. In another ovary of about the same age the glands are relatively 

 very large. Tho columnar cells are greatly elongated, their nuclei lie at the deeper or outer ends of the cells, and 

 the Ininen of the gland is often completely obscured. The gland forms a kind of egg tube, abutting upon and partly 

 inclosing the growing egg. The columnar cells stop short at the sides of the egg, so that the glandular cjeeum resem- 

 bles a narrow bag with an egg pushed into its mouth. The glandular cells are directly continuous with those of the 

 follicle. The axial portion of this ovarian lobe is composed of hollow spaces, blood sinuses, and loose stroma, in 

 which very young eggs occur. Degenerating cells occur not only in the strouia, but probably in the developing ova 

 also. In Peripatus Norir Zntlaniliw the yolk is described by Lilian Sheldon as arising not only from tho egg proto- 

 plasm, but also from the follicle cells (. r >7). 



When ten to fifteen days have elapsed after egg-laying (eggs in egg-nauplius stage), the gland-like bodies 

 have almost wholly disappeared. The wa,lls of the caeca are shrunken and crumpled, and the latter have been 

 crowded to the extreme periphery of the ovary. The ovary now contains a solid core of immature eggs, stroma, and 

 bloodvessels. This is continuous with radial sheets of similar tissue which extend from the center toward the pe- 

 riphery. The outer and more mature masses of ova are thus divided into more or less continuous, longitudinal bands. 



At a still later period (eggs with eye pigment, four to five weeks' old ) the glands are present merely as 

 shriveled remnants. Later still (lobster taken August 21 ; egg embryos in a late stage) there is no trace of gland-like 

 structures. In the ovary of a lobster (taken June 30), with eggs about to hatch, the condition is similar to the last. 

 It is now about eleven months since the eggs were laid, yet the diameter of the largest ovarian ova is only about our- 

 half that of the mature eggs. The ovarian wall is thinner than in previous stages, and in the axis of the. lobe there 

 are still sheets of very small, immature ova. 



It seems that the bodies which have been described as probable yolk glands are present in the peripheral 

 parts of tho ovaries only during the limited period of from two to three weeks after the eggs are laid, and when I In- 

 orgius are recovering from tho changes which follow this event. Their structure is quite unlike that of bloodvessels 

 or sinuses with which they are intricately associated, and their relation to the growing eggs seems to imply thai 

 they have some function to perform in tho nourishment of the peripheral ova. Their short existence, on the other 

 hand, might lead us to suspect that they were more or less rudimentary structures, or that they were concerned with 

 the secretion of the gluey substance with which the eggs are coated at the time they are laid. Their true function, 

 however, remains to be determined. 



Ovaries which I have examined, taken in summer (July) from lobsters ( " paper shells " ) which have reeenl ]y 

 moulted and which do not carry eggs, present very thin walls, and the largest ovum measures in diameter about one- 

 half that of the mature egg. These lobsters have probably hatched 

 moulted. (Compare the ovary of the lobster taken June 30 above.) 



Some allowance is to be made for individual difference, but the slow growth of the ovarian egg, which we, 

 have traced from the summer when eggs were laid to the following summer when these rg^s wen' hatched, is very 

 noteworthy, and shows conclusively that the lobster is not an anuual breeder. 



