DEVELOPMENT OP DTSTTGHOPOEA VIOLAOEA. 137 



pora (Hickson, 17), and the Stylasteridse (Hickson, 

 18 and 19). 



It is not my purpose to discuss fully the various views that 

 have been put forward concerning the origin of the Metazoa 

 from the Protozoa. The gastrula theory, the planula theory, 

 the plakula theory, and the phagocytella theory have each 

 received in their turn the consideration of naturalists, and 

 nothing would be gained were an attempt made in these pages 

 to reopen the discussions that they gave rise to. 



But I cannot pass on without expressing my opinion that 

 the developmental history of the Hydrocorallinse lends some 

 support to the so-called '' plasmodium " theory. Many years 

 ago, Jehring (27) and Saville Kent (32) put forward the view 

 that the Metazoa are derived from a multinucleated Protozoan 

 like Opalina. Sedgwick (57) has supported this view, as a 

 result of his important work on the development of Peripatus, 

 and considers that the ancestral Metazoan was probably of 

 " the nature of a multinucleated Infusorian, with a mouth 

 leading into a central vacuolated mass of protoplasm." 



In discussing Saville Kent's views Metschnikoff (42) says 

 that there is no evidence of the formation of such a multi- 

 nucleated cell in the lowest Metazoa. 



Now I have already pointed out that in the earliest stages 

 of the Stylasteridse and of Millepora the embryo is nothing 

 more nor less than a multinucleated cell; that is to say, it is a 

 single undivided mass of protoplasm, containing numerous 

 nuclei. It might be urged that it is a syncytium, a number 

 of cells fused together; but there is no more evidence for 

 such a view than for the view that it is a single multinucleated 

 cell. 



Similarly it may be urged that Tubularia (Brauer, 5 a), 

 Aglaophenia (Tichomiroff, 55), Alcyonium (Kowalewsky, 37), 

 Gorgonia (von Koch, 36), and Renilla (Wilson, 63) all pass 

 through a stage in their development in which the embryo is 

 simply a multinucleated cell. 



The fact that such a condition as this occurs in many 

 diflFerent groups of the animal kingdom widely separated from 



