56 



WHEELER. 



[Vol. VIII. 



surface. The resemblance of the "micropyle" to the indusium 

 is apparent at a glance {cf. Fig. 2, PI. I). I have followed the 

 organ in Aimrida through the later stages by means of sections 

 and find that it persists for some time as a simple thickening 

 of the blastoderm, still connected with the peculiar striated 

 membrane which stands away from the surface of '■the blasto- 

 derm at all other points. Finally, when the embryo has 

 become flexed dorsoventrally and the body-walls are closed, 

 it sinks into the yolk and is absorbed. 



Fig. V. 



Median section of the egg of Aimrida jnaritima. d.o., "micropyle"; bid., 



blastoderm. 



Although much simpler in its structure, I do not hesitate 

 to homologize this " micropylar " organ in Amirida and the 

 PoduridcE in general with the indusium of Xiphidiiim. A pos- 

 sible objection to this homology, on the ground that the indu- 

 sium arises on the ventral face of the Qg^, while the Podurid 

 " micropyle " is dorsal, has little weight, since the organ bears 

 in either case the same relation to the head of the embryo. 

 Provided, therefore, the egg of Aimrida were to acquire yolk 



