CRANGON VULGARIS. 7 



Asto the identity of the positiou ot' the blastopore, with 

 that of the anus, a word more may be said. The relations 

 of the mesoderm aiid especially of the entoderm cells, show 

 that the two openiiigs cannot be very far removed from 

 each other, as can be seen from a comparison of fig. 29 

 with figs. 8 and 9 of the precedingpart of the paper. Reich- 

 eiibach claims in Astacus ('86) that the anus is formed 

 a little in front of the place where the blastopore closed, 

 but his figures do not seem to me to fully support him in 

 this point. They rather seem to leave the matter undecided 

 as to absolute identity of position, with the chances in fa- 

 vor of an even closer approximation than the lettering of 

 his fig. 7a would indicate. For all that text or illustrations 

 indicate, the "leader " from "^," in the figure quoted, seems 

 to be arbitrary in position, while if the letters, "2%. Abd, 

 F" be rightly placed in his fig. 39, there is no room between 

 the blastopore and the abdominal flexure for the anus to 

 form. A comparison of these figures with his 49 and 50 

 do not help the matter in the least. Mayer, in his account 

 of the development of Eupagurus ('77),^ thinks that the 

 anus forms in the position where the blastopore closed, 

 while the fact that Bobretzky at first stated that the blasto- 

 pore persisted, as the anus, a statement which he later cor- 

 rected ('74, p. 186) , — shows that the two in Astacus must 

 be nearly, if notquite, identical in position. Still Reichen- 

 bach's Statement (e. g. '86, pp. 42 and 43) is very explicit, 

 and should not be set aside without more evidence. 



Entoderm. — The entoderm cells at this stage are com- 

 paratively few in number. They are sparsely and very ir- 



^ Mayer says in effect {I.e., p. 237), that iiivagination gives rise, not 

 to a true entoderm but to both proctodeal and entoderinal tissue. The 

 whole of the hind-gut arises from the invagination, while the cells, 

 which bud from the invagination and pass iuto the yolk, form the ento- 

 derm. This of course is confirmative of the view quoted in the text. 



