DEVELOPMENT OF LIMULUS POLYPHEMUS. 157 



cells become indefinite in form, tlie nuclei disappear, and a stroma is formed, probably from 

 the breaking down of these cells. From these epithelial cells arise the eggs (fig. 2), which 

 thus originate from what cannot be optically separated from true epithelial cells, as ob- 

 served by Gegenbaur. But along some of the tubes runs a sort of fold or ruffle, consisting 

 of clear, non-nucleated cells (unless the nuclei were concealed Ijy the overlapping cells), 

 which project out from the edge of the fold (fig. 2, b). These also are apparently des- 

 tined to become transformed into germinative vesicles, and subsequently eggs. They are 

 elongated, crowded together, clear, pellucid, with a few molecules at the base of the cell. 

 They pass gradually into the ordinary epithelial cells, whicli are smaller than those about 

 the base of the fully formed cell-egg (fig. 2), and are entirely filled with molecules. Near 

 these cells (fig. 2, b) were larger ones (fig. 2, c) easily detached from the stroma, spheri- 

 cal, and filled with molecules, but with a clear nucleolus. On becoming larger the nucleo- 

 lus is filled with molecules, as at fig. 2, d, which are much darker than the molecules in 

 the other part of the cell. Up to this time the contents of the cell-egg consist of proto- 

 plasm alone. The stage represented by fig. 2 is signalized by the formation of a layer of- 

 protoplasm (fig. 2,|j?) around the germinative vesicle, and afterwards by the appearance of 

 the fat or yolk granules, or deutoplasm. Less perfectly formed yolk granules are seen in the 

 nucleus of the cell-egg. In another cell-egg farther advanced (fig. 3), the nucleus is more 

 distinct, that portion of the wall of the egg situated within the pedicel being more readily 

 seen than before. (Its distinctness in fig. 2 is exaggerated in the plate.) The molecules 

 of the nucleolus are glistening or refractive bodies, and form a clearly defined, central mass, 

 leaving the periphery clear. 



The' yolk granules are still clearer in other specimens (fig. 4), and in still others the cell- 

 egg becomes more easily detached, and the yolk granules have increased in size, until, as in 

 fig. 5, one or two are seen to be as large as the germinative vesicle. After this, the princi- 

 pal changes in the egg are the multiplication of the yolk granules, and the thickening of the 

 egg membrane itself to form the thick, dense chorion. No yolk skin was observed, neither 

 any niicropyle. ^ 



Formation of the Blastoderm. The eggs received during the second season had been 

 laid several days, at least three or four, and the mode of formation of the blastoderm 

 could not be seen. In endeavoring, therefore, to artificially impregnate the eggs of Limulus, 

 the following appearance was observed. Six hours after the operation the surface of the 

 yolk was seen to be covered with little balls of yolk cells projecting out, with deep spaces 

 between them ; the masses of cells being round, and not crowding on each other. I could 

 not see whether these masses enclosed nuclei, owing to the opacity of the yolk. In 

 twenty hours after the operation, the eggs, under a power of thirty diameters, were seen to 

 be smooth again, and the surface covered with a layer of very indistinct pale cells (fig. 6, 



I Gegenb.aur remarks that he detected no yolk-skin (dotter- In the eggs loosened from their pedicels the scar thus 



haut) ; and besides the cuticida of the egg-cell itself, in the egg formed appears Uke a micropylar opening. But in ripe eggs 



in the stage observed by him at least, no special membrane this opening becomes closed before the egg is laid. His ob- 



traceable to a cellular membrane was observed, so that here servations were made on what he regarded Limulus molucca- 



occurs a case where cells at an earlier stage are provided nus, though it came from the Antilles, and he thinks it could 



with a membrane (such as covers the epithelial cells of the not be L. Pohjphemus. I am not aware, however, that any 



tubes of the ovary), which afterwards disappeai-s (through other species than L. Pob/phcmus inli.ibits the AVest Indies, 



resorption?) and then goes back to a lower stage of develop- I have found it frequently at Key AVest, Florida, and find 



ment. Indeed the cell undergoing this transformation ac- that it does not differ from specimens from Beaufort, N. C, 



qi;ires a new significance ; it becomes an egg. Massachusetts, and Maine. 



MEMOIRS EOST. SOC. SAT. HIST. VOL. II. 40 



