138 THE DEVELOPMENT OF 



A reconciliation of tlie difFerences will only be possible 

 upon the publication of figures and a detailed account of 

 the processes in Oniscus and Androctonus. 



The observations on the relations of the mouth and anus 

 to the blastopore in the Crustacea are extremely fevv. 

 Reichenbach's account of Astacus ('86) is by far the most 

 complete and conclusive, and there the anus is clearly in 

 front of the position of the blastopore. Ishikawa ('85) 

 has the sanie result in Atyephyra ; and in Crangon, 

 though not certain, I still think that the anus occupies a 

 similar position with reference to the blastopore. In none 

 of the Crustacea do we find that elongate blastopore 

 (primitive groove) which is so characteristic of the tra- 

 cheate arthropods and the fact that the blastopore entirely 

 disappears before the appearance of either permanent 

 opening of the digestive tract renders it rather difficult to 

 trace their general relationships. Reichenbach's studies 

 and his figures ('86, pls. II and III) seem to be conclusive 

 upon the point that there is no proliferation which would 

 extend the limits of the circumblastoporal cells as far 

 forward as the point where the mouth is formed or even 

 far eiiongh to include the anus. 



In Crangon I have been unable to recognize but one 

 kind of mesoderm and that is not differentiated until gas- 

 trulation. It arises, as numerous sections show, fromthe 

 edge of the blastopore and from no where eise. Bo- 

 bretzky recognized but one kind of mesoderm in Palse- 

 mon, butthisarose from cells clearly endodermal. Reich- 

 enbach ('77 and '86) has a secondary mesoderm which 

 is budded from the true endodermal cells after the process 

 of gastrulation is completed. Ishikawa, in Atyephyra, 

 also has two kinds of mesoderm, one arising from the 

 edge of the blastopore ; while the other arises from the 



