230 Chas. W. and G. T. Hargitt. 



he able to find any proof for Goette's assumption that the immi- 

 grated cells took an active part in entoderm formation; hence he 

 believes Goette to be incorrect in this point. Concerning these 

 same cells Hein refers to the statements made by Hyde that, the 

 nuclei were usually broken into small fragments and scattered 

 through the cell, and to the observations of Smith that no such 

 cell ever had an intact nucleus. Hein concludes that such frag- 

 mented nuclei '' . . legen wohl einen Zerfall der Zellen zum 

 mindesten nahe." 



More recently Conklin (1908) has studied Linerges mercurius. 

 The eggs are deposited about 8 a.m. in masses surrounded by 

 jelly. Polar bodies form typically, the sperm enters at the vegeta- 

 tive pole and moves to the animal pole where it fuses with the 

 egg nucleus. Cleavage begins at the animal pole and at the end 

 of the first cleavage there is a small space between the two cells 

 which is the first indication of the cleavage cavity. The second 

 cleavage is meridional, the third equatorial and both begin in the 

 center of the egg and pass outward. The animal pole becomes 

 the ectodermal pole, the vegetal the entodermal. Gastrulation is 

 usually by invagination, though sometimes an ingression of cells 

 from the vegetal pole fills the cleavage cavity, and the archenteron 

 only later forms by a splitting apart of the cells. The end result 

 is the same in the two cases, and this Conklin believes is an indi- 

 cation of the close relationship of unipolar ingression and invagi- 

 nation. 



From this review it will be seen that the chief controversy 

 with regard to the early development of the Scyphomedusse has 

 centered in the method of gastrulation. The differences in cleav- 

 age have been found rather insignificant and the results of gas- 

 trulation have in every case been the formation of a typical two 

 layered planula. The main reason for the strict adherence to a 

 belief in one or another single mode of gastrulation by some of 

 the disputants appears to rest upon the belief that one mode must 

 be more primitive than another; that there would be different 

 phylogenetic relations indicated if this, rather than that, method 

 were more common. 



As early as 1881, Haeckel showed that there were marked varia- 



