DEVELOPMENT OF LIMULTJS POLYPHEMUS. 159 



of Gammarus ; the yolk, as in these animals and all the insects, not undergoing segmen- 

 tation. 



The next changes in the eggs (observed May 27th, the day the eggs were received from New 

 Jersey,) were not apparently of much consequence as regards the blastoderm, or formation of 

 the germ, so far as I could ascertain. The peripheral yolk granules became collected into 

 irregular white flake-like masses, varying greatly in size, and giving a rough outline to the 

 yolk. Hundreds of these eggs presented the appearance indicated by fig. 6 b. The whit- 

 ish flakes after awhile unite together as seen in fig. 7, and at the lower left side a laro-e 

 white mass is seen, formed by the union of these flakes. They thus unite together and dis- 

 appear, the lumps flattening down, the contour of the yolk being again nearly as regular as 

 before, while the yolk fills out the egg, the space between the chorion and yolk being 

 greatly diminished. Usually one or several of these balls of yolk granules remain on the 

 surface of the yolk, and may be seen after the germ appears, as at fig. 14, x. They 

 become finally detached from the yolk and situated between the blastoderm skin and the 

 chorion. In certain eggs they looked like rudiments of limbs, which I took them to be last 

 year,^ when the batch of eggs received from Mr. Lockwood had nearly all passed thi-ough 

 this stage and the germ had developed. 



The eggs after the flattening down and disappearance of the white spots, remain without 

 farther perceptible change about a week before the germ or primitive disk appears so as to 

 be visible. During this time the blastodermic skin ("amnion") is formed. The surface of 

 the yolk is covered with irregularly hexagonal cells (fig. 8 a). In outline (fig. 8, profile 

 of fig. 8 a,) they are seen to be spherical and filled with granules. They may be easily 

 seen by reflected light with a triplet, and form a distinct layer resting immediately on 

 the yolk. I could detect no nucleus in them. 



Notwithstanding the apparent absence of nuclei I believe that these cells may be 

 compared with the blastoderm cells of insects, as I have observed them in the Hymenop- 

 tera {Nematus ventricosus), the Coleoptera [Attelabus rhois), and the Diptera (Pulex 

 felis), and as they have been previously observed in the Hymenoptera, Diptera, Coleop- 

 tera, Hemiptera, and Neuroptera (Libellulidae), and Scorpions by various embryologists, 

 especially Weissman, Metznikow, Melnikow, Brandt, and Ganin. The blastodermic skin, or 

 " protoderm," of Limulus, as will be seen fixrther on, is moulted essentially in the same 

 manner as in the scorpions and the hexapodous insects, and in all respects, both in its 

 structure and function, it seems homologous with the protoderm of the class of insects so far 

 as the orders have been observed.^ Indeed Prof. E. Van Beneden remarks the "first 



^ The statement In the report of my remarks before the '^Dohrn says (Humphrey's Jour. Anat. and Phys., 1867) 



Association, and in the abstract printed in the Proceedings that "the 'amnion' of Scorpio is nothing but the carapace of 



of the American Association, 1871, p. 247, that "one or two Zoea. So the amnion of insects is nothing but the carapace of 



eggs were observed in process of segmentation" is entirely Zoea." Having as I think demonstrated tliat the "amnion" 



erroneous. The specimens were addled. So also must the of Limulus is in all respects homologous with the "amnion" 



statement that at first one pair, and afterwards three pairs of of insects, (and as we shall see farther on that it protects the 



limbs appear, be cancelled. The six pairs of limbs as reprc- embryo of Limulus while in the zoea condition), how it can be 



ented in fig. 12, appear all at once. I was misled by the homologous with the zoea carapace I am at a loss to see. 



peculiar arrangement of the whitish masses on the surface of So far as regards the amnion of insects and Crustacea, the 



the yolk. The inspection of a large number (several hun- two classes of articulates are parallel, it being present in 



dreds) of eggs in an earlier stage than in those observed in both, and one class can hardly be considered in this respect 



1870 has enabled me to correct these errors. as descendants of the other. 



