142 THE DEVELOPMENT OF 



pis. I and II) has them well differentiated in Astacus even 

 before invaginatiou begins. Again, Reichenbach has the 

 nuclei of the optic lobes and the two halves of the tho- 

 racico-abdominal region exhibiting a marked concentric 

 arrangement. This I have not seen in Crangon. Besides 

 these points and the relatively greater distance in Cran- 

 gon between the optic and thoracico-abdominal lobes, and 

 the smaller number of cells (a necessity from the much 

 smaller size of the egg) our results compare favorably. 



Mayer, in his studies of Eupagurus ('77) did not go 

 into such detail as Reichenbach, as he did not trace the 

 cells in his earlier stages. His figures 14 and 15 com- 

 pare well with that of Crangon now under discussion, ex- 

 cept he does not figure the cords connecting the optic 

 lobes (Kopfanlage) with the thoracico-abdominal area. 

 In Crangon, these cords are fainter than the rest of the 

 germ, and hence they may have existed in Eupagurus 

 but have escaped observation. In other respects the 

 shape of the thoracico-abdominal region and the distance 

 between this and the optic lobes there is a close resem- 

 blance between these two forms. 



Accepting -the terminology which Ishikawa applies to 

 his figures of the early embryos of Atyephyra ('85, pi. 

 XXVI, figs. 55 to 59) it is not easy to reconcile his results 

 with mine. It would seem, however, that his mandibles 

 and abdomen are not in reality such but that together they 

 form the thoracico-aBdominal region. There is, however, 

 not sufficient evidence to decide this point as the stages be- 

 tween these figures and his figure 60 are lacking. If 

 this view be the true one (his mandibles being but the 

 lateral expansions of the thoracico-abdominal region) his 

 results will compare well with those of Reichenbach and 

 Mayer as well as with my own and we shall be relieved of 

 the difficulties surrounding the appearance of the mandibles 



