6o KINGS LEY. [Vol. VII. 



of the Japanese King Crab (Z. longispind), which presents some 

 points of difference from the L. polyphenms of the Atlantic 

 coast. Some of these variations may be noticed here. 



In the external development Kishenouye did not distinguish 

 between primitive cumulus and posterior cloud. In the process 

 of metamerism the first line of demarcation occurs between 

 somites I and II, while the appearance which I have called the 

 primitive streak does not occur until two somites are differen- 

 tiated from the anterior and posterior areas. In the later stages 

 he finds organs homologous with the flabellum of appendage VI, 

 occurring as transitory rudiments on somites 2-5. These are 

 clearly not homologous with the peculiar (sense .'*) organs men- 

 tioned on p. 49, since the latter occur outside the ventral disc, 

 while the flabella of Kishenouye are all within that area. 



In the internal development the discrepancies are more im- 

 portant. Thus Kishenouye describes the ectoderm as separat- 

 ing from lower-layer cells, and says that the mesoderm has 

 three origins : (i) from the lower-layer cells, (2) from the 

 edges of the primitive streak, which is confined to the posterior 

 portion of the ventral disc, and (3) from cells in the dorsal 

 region which migrate from the yolk. The primitive streak 

 mesoderm is confined to the abdominal region, while that 

 derived from the lower-layer cells gives rise to the tissues of 

 the cephalothorax. 



A still farther point of difference is with regard to the meta- 

 stoma. This Kishenouye regards as a true appendage serially 

 homologous with the other appendage of the body. In this 

 I cannot agree with him. My observations show no metastomal 

 somite and no corresponding neuromere.^ On the other hand, 

 it seems probable that there is here an error in interpretation, 

 for a study of his figures inclines me to believe that his meta- 

 stoma is in reality the operculum, and that the following appen- 

 dages are to be correspondingly changed. The other points of 

 difference will be discussed in the second part of this paper. 



Turrs College, Mass., August, 1892. 



1 See Kingsley, '85, p. 532, PI. XXXVIII, Fig. 22. 



