378 ARTHUR T. MASTKRMAN. 



Eoule's paper is unaccompanied by any figures, luid is of 

 the nature of a resume. He has followed the segmentation 

 to the stage with thirty-two blastomeres, in which he states 

 there is no blastocoele. The spherical blastula spreads out 

 laterally to a discoidal shape, which then iuvaginates and 

 hence becomes globular. The blastopore is at one of the 

 poles of the gastrula, but becomes eccentric by differential 

 growth. He finds no raesoblast till the mouth and pre-oral 

 hood over it are established, thus differing from Metschni- 

 koff and Foettinger, and indeed from Kowalevski. From 

 this stage onwards he finds primary mesenchymatous cells in 

 the blastocoele. Later still, the " mesendoblast" in the 

 neighbourhood of the anus proliferates to form the initial 

 " mesoblastiques." The cells of these break up partly into 

 single cells, which join the mesenchyme already referred to, 

 and partly form two compact masses which Roule considers 

 to be the mesoblastic bands (homologous to those of the 

 trochophore). Roule does not state his methods of investiga- 

 tion, though it would be difficult to determine with any 

 certainty the points above described without serial sections 

 of the embryos. 



Lastly, Schultze (16) has quite recently (1897) published a 

 short paper upon the development of the Ph or on is found in 

 the Black Sea. He found that the blastula became bilateral. 

 As in the case of Koule and Metschnikoff, he describes the 

 mouth as formed from the blastopore, the anus beiug a new 

 formation. He, like Metschnikoff, finds single mesoderm 

 cells in the blastocoele of the blastula stage. They arise 

 from the endoderm, and later become pressed into the pre- 

 oral lobe and the anal region, eventually arranging them- 

 selves into somatic and splanchnic layers. 



He illustrates this process by figures, but does not in any 

 way refer to his methods. He attempts to account for 

 Roule's and CaldwelPs descriptions as being due to the per- 

 sonal element and the influence of Hertwig's coelom theory. 

 He also remarks that Caldwell evidently mistook the ventral 

 invagination which gives rise to the adult body for a pair 



