98 EICHARD EVANS. 



possible that those who hold this view of the origin of the 

 gennnule are mentally dominated by the principles of the 

 " Germ Layer Theory." If so, this would be a splendid 

 example of an otherwise good theory leading to false conclu- 

 sions. Further, it is more than probable that Carter, Lieber- 

 kiilin, and Goette never saw the first signs of the formation 

 of the gemmule. This is undoubtedly the most charitable 

 view to take of the conclusions they arrived at. 



Now that the above-mentioned views have been disposed 

 of, there remain for consideration two more views, one of 

 which can be set aside after only a few remarks. The view 

 in question is the one according to which the gemmule is 

 derived from a group of cells, all of which are alike. This 

 view has not found favour with those who have investigated 

 the structure and formation of the gemmule. Carter at one 

 time held it (5), thinking that the gemmule was an ovarium 

 of a " Spongozoon," a name which he gave to his imaginary 

 sponge-animal. However, in a later publication he gave his 

 support to another view. In fact, a single glance at a good 

 section of the gemmule during some of the early stages is 

 enough to cause one to recoil from the idea that only one 

 class of cells take part in its formation. Consequently there 

 remains only one view, namely, that the gemmule originates 

 from a number of cells belonging to various classes. This 

 view, in one form or another, is supported by Marshall (15), 

 Wierzejski (19), Zykoff (21), and Weltner (18). 



Marshall's account does not concern us as much as those of 

 the other authors above mentioned do, for the reason that he 

 Avorked on the gemmule of a species belonging' to a different 

 genus. There is, however, one point which must be men- 

 tioned. The point in question is that he derives the gem- 

 mules from two classes of cells at least; namely, the cells 

 which he terms '^ trophophores," and which give rise to the 

 contents of the gemmule, that is the reproductive part, as 

 well as to the delicate structureless membrane surrounding 

 it ; and the " mesoderm " cells, which give rise to the outer 

 shell as well as to the spicules. The importance of this dis- 



