CRANGON VULGARIS. 5 



iieed revision. He gives a transverse section of his eni- 

 bryo, the figiire closely resembling fig. 31 of the present 

 paper, and refers to the deeper cells as mesoderm. If they 

 arise, as he claims, by bndding from the onter layer cells, 

 it is probable that he is dealing with nervons, rathcr than 

 mesodermal, tissnes. It is, however, more probable that 

 in Mysis, as in otlier forms, these are true mesodermal cells 

 and have attaincd their present i^osition by a forward growth 

 in the same way as will be presently described for Crangon. 

 The täte of the vitellophags will be mentioned later. 



The observations of F. H. Herrick ('86) upon the de- 

 velopment of Alphens record a state of aflfairs, so far as 

 gastrulation and origin of the mesoderm are concerned, 

 which is readily comparable with that of Crangon. 



Dr. A. T. Brnce, in his complete paper ('87) , is more in 

 accord with the Hertwigs, than was apparent in his prelimi- 

 nary commnnication ('86) referred to in the secondpart of 

 this paper. In regard to the formation of the entoderm in 

 Thyridopteryx, this is even more so than in the other forms 

 which hestndied. He regards, in all forms, the yolk cells 

 as true entoderm, with vitellophagous functions, and be- 

 lieves the functional entoderm to be of later origin. 



Keinhard has recently ('87) restudied Porcellio scaber, 

 and his results are in tair accord with the Interpretation of 

 Bobretzkj-'s researches given in the preceding part of this 

 paper. Reinhard concludes that the egg-nucleus divides, 

 and that some of the resulting nuclei, with a portion of the 

 protoplasm, form amoeboid cells, which gradually creep to 

 the surface. The resulting blastoderm, is not at first con- 

 tinuous, but consists of " Islands " (c/. Bobretzky, '74, pl. 

 XXI, ligs. 3 and 7). The undifferentiated cells, which re- 

 main behind, form the primary entoderm, which soon be- 

 comes differentiated into ento- and mesoderm. 



Cholodovsky ('88) says that, in Blattet germanica, the 



