260 H. J. VAN CLEAVE 



the point wherein the Eorhynchi differ most essentially from other 

 Acanthocephala lies in the fact that the nuclei of the mature 

 worms in this genus are derived directly by the differentiation of 

 the embryonic nuclei, while in the other genera there is intro- 

 duced a period of indeterminate fragmentation of the nuclei 

 at the time of the formation of the adult organs. In view of these 

 facts the writer maintains that the term cell constancy is fully 

 justifiable when dealing with the structure of the Eorhynchi, for 

 each nucleus with the cytoplasm surrounding it represents a cell. 

 Moreover the introduction of a wholly different term in the consid- 

 eration of phenomena identical with those grouped under the 

 head of cell constancy would but add confusion to the subject, 

 for after all the wall is not the essential part of the cell. 



PROOFS OF CELL CONSTANCY IN THE GENUS EORHYNCHUS 



1. Cuticula 



The cuticula of the Eorhynchi is a thin, homogeneous, layer 

 covering the entire body. Even under a magnification of nine 

 hundred diameters no specialized structure is visible. By virtue 

 of its noncellular structure this body covering is readily eliminated 

 from consideration in this connection. 



2. Subcuticula 



The subcuticula, which comprises by far the greater part of the 

 body wall (figs. 4, 5 and 23 s), lies directly under the cuticula. 

 While the general structure of this tissue in the Eorhynchi closely 

 resembles that of other genera of Acanthocephala, the arrangement 

 of the nuclei is decidedly distinctive of this genus. Another feature 

 wherein these forms vary from their near relatives is that the com- 

 ponent layers of the subcuticula are not as clearly defined as in 

 many other genera. O. F. Miiller in 1780 (plate 61) figured Eo. 

 rutih (Mtill.) and in the body wall showed five 'oscula,' as he 

 called them later (1784), four of them on the dorsal side of the 

 body and a single one on the ventral side near the anterior end. 

 There can be no doubt that these structures are the giant nuclei 



