594 MORGAN AND HAZEN. [Vol. XVI. 



closes later than in the Messina form, as described by Hat- 

 schek. We have had material from both localities and can 

 state that the difference was the result of less normal devel- 

 opment in the Neapolitan form. Sobotta has been unable to 

 decide how the axis of the gastrula is related to the axis of 

 the embryo. He believes that the blastopore closes equally 

 from all points and that no concrescence takes place. 



MacBride ^ and Sobotta have entirely overlooked the pres- 

 ence of smaller and lighter cells over the dorsal wall of the 

 archenteron, and in consequence MacBride says that " it is dif- 

 ficult to find words to adequately characterize the artificiality 

 and arbitrariness of such a view." 



MacBride continues : " If we examine a transverse section 

 of a completed gastrula, ... we find no difference in character 

 between the cells forming the dorsal wall of the alimentary 

 canal and those forming the ventral wall, such as we should 

 have the right to expect did Lwoff's hypothesis in any way 

 correspond with the facts." This statement is unquestionably 

 wrong, as our figures show. 



MacBride gives an inadequate account of the process of gas- 

 trulation : " Thus I regard the gastrulation as a fairly uni- 

 form pushing in of the under or flattened surface of the 

 blastula, accompanied by division and multiplication of the 

 cells, such multiplication being at first most active in the dor- 

 sal (future anterior) lip of the blastopore. The blastopore, 

 which is still wide, becomes rapidly narrowed by the upgrowth 

 of the ventral lip ; in contradistinction to what Hatschek 

 asserts, the dorsal lip remains relatively stationary." ^ 



No evidence is offered in support of this opinion, which is, 

 as we have tried to show, incorrect.^ 



It is not our intention to enter into a comparison of the gas- 

 trulation of Amphioxus and of the other Chordata. The resem- 

 blance of the early larva of the Ascidians to that of Amphioxus 

 is, however, so close, that a few words seem justified on this 

 topic. The recent paper by Castle on " The Early Development 



1 MacBride, p. 597. 2 j^id., p. 591. 



3 MacBride's Fig. 10 shows the endoderm of the dorsal lip of the blastopore 

 continuing into the ectoderm on the outer side of the nerve tube. 



