No. 2.] MICRODEUTOPUS GRYLLOTALPA COSTA. 321 
Il est indubitable que chez les Gammarus et de plus chez les 
Orchesties l’organ dorsal, ainsi que l’ectoderme avoisinant, 
détachent de cellules; leur nombre n’est pas grand, elles sont 
tout a fait liberées et s’enfoncent dans le vitellus nutritif. 
Or, tandisque les cellules en question se logent dans les masses 
vitellines, les cellules entodérmiques, d’une parfaite ressemblance 
avec les premiéres, sont aussi en voie d’y chevaucher; leur 
résidence simultanée dans le vitellus ne nous permet d’affir- 
mer aucunement que les cellules issues de la plaque dorsale 
s’atrophient; aucune de mes préparations ne le prouve pas.” 
I think the plaque of cells from which, Dr. Pereyaslawzewa 
writes, no organ is derived is the dorsal organ, and what she 
calls the dorsal organ is the entodermal invagination. At a 
later stage a cavity is found in the dorsal organ in Microdeuto- 
pus which agrees, in this respect, with what Korotneff found 
in Gryllotalpa. The characteristic appearance of the dorsal 
organ cells led me to recognize the plaque of cells as the dorsal 
organ. Dr. Pereyaslawzewa, it would seem, occupies the middle 
ground between Ulianin (81), who supposes the entoderm is 
derived from the dorsal organ alone, and Bergh, who derives all 
the entoderm from the ventral plate. Bergh does not hold that 
the entoderm is formed at many points on the ventral plate, 
as Dr. Pereyaslawzewa holds, to judge from her figures, but 
he supposes that “vielmehr entsteht dasselbe durch Einwuch- 
erung von Blastodermzellen an einer bestimmten Stelle die 
also dem Blastoporus entsprechen diirfte.” In his figures Bergh 
marks the cells in the second layer of the ventral plate, in the 
naupliar region, ez. My own results agree with those of 
Ulianin, who believes that a// the cells in the second layer of 
the ventral plate give rise to mesoderm, and that oly the cells 
carried in by the dorsal invagination form the entoderm. It 
would seem, then, that as far as the entoderm is concerned the 
amphipod agrees most nearly with what Bobretzsky has found 
to be the case in Palaemon, according to the statement of 
Heider. 
