138 SYDNEY J. HTCKSON. 



one other also lends support to the view that it may have 

 some important phylogenetic significance. 



Instances of the occurrence of an unsegmented multi- 

 nucleated Plasmodium are found not only in the Coelenterata 

 above mentioned, but in Peripatus^ Myriapods, Spiders (Kishi- 

 nouye, 34^ and Morin, 44), Insects, Crustacea, Elasmobranchs, 

 and probably many other forms with large eggs. 



It might be urged as an argument against the plasmodium 

 theory that the multinucleated plasmodium occurs principally 

 in the development of those forms whose ova contain a large 

 amount of food-yolk, that the segmentation is modified by the 

 presence of this yolk, and that consequently the phylogeny is 

 obscured. 



But it does seem to me that in the ovum that is perfectly 

 clear and homogeneous we have a cell that is any nearer to the 

 ancestral Protozoan than the ovum that contains a moderate 

 amount of yolk. 



It is almost certain that the ancestral Protozoan normally 

 contained some food-vacuoles, and it is quite as probable as 

 not that it had some contractile or simple water-vacuoles for 

 floatation purposes as well. 



It is quite as reasonable to suppose that the Metazoa are 

 derived from an Actinosphserium-like ancestor with vacuoles in 

 the outer regions as well as in the inner mass, as it is to derive 

 the Metazoa from a " multinucleated Infusorian with a mouth 

 leading into a central vacuolated mass of protoplasm." 



If this is the case, then we can no longer consider the yolk- 

 bearing eggs to be secondarily modified, and the small 

 transparent eggs to be the primitive types from which all the 

 others are derived; but we may expect to find in the develop- 

 ment of eggs with a moderate amount of yolk just as much or 

 even more evidence of ancestral history as in eggs that are 

 practically yolkless. 



It must not be forgotten, moreover, that the occurrence of a 

 multinucleated plasmodium is not confined to those cases in 

 which the ovum contains a large amount of yolk. 



In the ovum of Millepora there is no yolk, and yet the 



