McCrady.] 178 [April 18, 



embryo; manifestly, however, for no other reason than that the trans- 

 parent contents are of unknown nature. The phenomena, however, 

 indicate the existence of an agency which controls the position of 

 the segment spheres, which would not of themselves, merely as bits 

 of protoplasm, become compressed together so as to have their form 

 mechanically changed, nor arrange themselves in regular form as a 

 blastoderm about a cavity, nor subsequently invaginate one part of 

 this blastodermic shell within the other to form a "gastrula." 



20. An agency capable of producing such special effects must be 

 either an attractive and repulsive (i. e., a selective or polar) force 

 residing in the segment spheres themselves, as magnetism is supposed 

 to reside in a magnet; or it is a protoplasm in which the segment 

 spheres are embedded, as the " cells " of Actinophrys are embedded 

 in the granular protoplasm which occupy their interspaces, and whose 

 extensions constitute the radially arranged pseudopodia. Such a 

 protoplasm would, however, differ from that of Actinophrys, in the 

 fact that it must be entirely diaphanous and devoid of granules; 

 identical, perhaps, with the clear protoplasm already alluded to 

 (§ 12), and which Carter called Diaphane. 



21. Under this theory the preference has been given to the latter 

 hypothesis, as obviating the introduction of polar attractions between 

 segment spheres, and necessitating only the assumption that in the 

 appropriation of the yolk by the amoeboid protembryo, while one 

 portion of its protoplasm is specialized in the process of investing 

 and cutting up the yolk into the small segment spheres, and so laying 

 the basis of cellification, the remainder is retained in an unspecialized 

 condition as a living and controlling matrix for the segment spheres 

 thus formed. 



22. If, therefore, the protembryo may be legitimately regarded as 

 an amceba-like being, the blastodermic holoblast may be regarded as 

 a stage of development analogous to Actinophrys ; while under this 

 theory all meroblasts are forms in which the protembryo first encloses 

 the yolk, and the Actinophrys stage is inaugurated primarily only at 

 one point whence in ever widening zones it gradually extends itself 

 over the whole yolk, its extension being perhaps really no growth of 

 the blastoderm, but a gradually extending conversion into blastoderm 

 of the protembryo which already encloses the yolk. 



23. During all these processes, the protembryo is of course sup- 

 posed to be assimilating food and growing, so that its quantity 



