Hyatt.] 70 [March 5, 



with refractile grains. Precisely similar stages with a nucle- 

 olus were observed in H. distorta, and also in one example 

 two ova were included in one chorion. A similar nucleus 

 filled with refractile granules appeared also in Chalinula limbata. 

 The nucleus then grows very large in Halichondria, still filled 

 with the refractile grains resembling the original nucleolus, and 

 the plasma in its turn does not increase so rapidly in size. The 

 nucleus expands until it occupies the entire cell, leaving only 

 a shallow zone of plasma, and this granular body almost entirely 

 filled the cyst of one ovum before segmentation occurred. 

 Theie were more or less granules in the vitellus, at all stages, 

 but these were sparsely distributed in the hyaline plasma and 

 the outline of the nucleus was never obscured, or indistinct; 

 the nucleolus, however, disappeared entirely as soon as the gran- 

 ules appeared in the nucleus. 



In all the tissues examined there has been a curious scarcity 

 of the structureless plasma or synctium of authors. We have 

 frequently, especially in Chalinula arbuscula thought we saw 

 a structureless intercellular substance, but it has always upon 

 more minute examination been resolved into cells or closely set 

 granules. In Chalinula living, frozen, or in alcohol, this was found 

 to be the case and though the methods of preparation were not 

 sufficiently varied to be determinative, the existence of such a 

 large amount of unorganized plasma in the mesoderm as is 

 usually figured seems to me at least in Chalinula to be unlikely. 

 It is interesting to note that Ganin has arived at similar results 

 in Spongilla. "Das mesoderm dt j r Spongilla kann nur als eine 

 einfache Form von Bindegewebe betrachten, in welcher die zell- 

 igen Elemente pravaliren und die structurlose, gallertige Grund- 

 substanz sehr gering entwiekelt ist." (Zool. Anz. no. 9, p. 198.) 

 In all the marine species, except Chalinula, my observations 

 showed that the granular plasma, which is not by any means a 

 structureless synctium, was prevalent in the mesoderm and this 

 layer presented quite a different aspect from that of Chalinula. 

 It is possible that this membrane may have different aspects in 

 disease or at different seasons, or under the action of distinct 

 reagents. Judging from the abnormal larvae and the tissues we 

 have seen, we should suspect a considerable range of variation, 

 much more than has been figured. 



