CELL CONSTANCY IN THE GENUS EORHYNCHUS 269 



gated and less regular outline of each nucleus in the fully mature 

 animal. At the same time this variation in shape is accompanied 

 by just as striking a difference in the manner in which the chro- 

 matin material is distributed. While in the adult the chromatic 

 substance is arranged in a more or less irregular branching figure 

 in the midst of the nucleus, in the immature condition the chro- 

 matin is more evenly distributed throughout the nuclear mass. 



Ij.. Proboscis and proboscis receptacle 



While ordinarily the proboscis and its receptacle are considered 

 as two separate organs or regions in the Acanthocephala, in the 

 following it seems better to consider the two together, since cer- 

 tain structures are not limited to either but extend through both. 

 Even though the proboscis shows practically no individual vari- 

 ation within the species, yet the different species may vary to a 

 remarkable degree. On the other hand, several species of this 

 genus present such slight variation in this organ of attachment 

 that the only evident point of contrast is in the relative size of 

 the various rows of hooks. In spite of the considerable range of 

 shapes and structures in different species, the following analysis 

 will show that in all probabiHty the same nuclei contributed to 

 the formation of structures which are distinctly different in one 

 group from those found in closely allied species of the same genus. 

 In other words, it seems that during the processes of differentia- 

 tion variations may have occmTed in the resulting structures but 

 that the cellular elements entering into the differentation were 

 the same in number in each species. 



At the tip of the proboscis (figs. 6 and 38 po.) is a structure of 

 questionable function and of variable form within the genus. 

 This structure, which occupies the central region of the proboscis, 

 is, in some species, an elongated cylindrical sac while in others it 

 more nearly approaches a globular form. Various functions have 

 been ascribed to this peculiar mass of tissue. Lespes ('64) con- 

 sidered a similar structm-e in Echinorhynchus clavaeceps as 

 the indication of an alimentary canal. Of a similarly located 

 structure made up of two cells in E. proteus Baltzer ('80, p. 26) 



JOURNAL OF MORPHOLOGT, VOL. 25, NO. 2 



