CELL CONSTANCY IN THE GENUS EORHYNCHUS 271 



axis of the body. However it does not seem necessary to do more 

 than mention that this abnormal or unnatural position is simply 

 the result of the action of an external physical force and for 

 this reason would not come under the consideration of abnormal- 

 ities of location such as were discussed under the nuclei of the 

 subcuticula. 



A dense chromatin mass lies in the center of each of these 

 nuclei. This mass at times is distinctly oval, again it may be 

 irregularly branched, and finally it frequently appears as several 

 smaller rounded masses scattered throughout the nucleus. In 

 this same species a pair of small nuclei occurs in a clearly demarked 

 area at the base of the terminal organ of the proboscis. These are 

 usually almost perfectly spherical, but at times they assume a 

 slightly ovoid shape (fig. 7). 



Eorhynchus longirostris. In this species (figs. 22 and 26, po) 

 the nuclei of the terminal proboscis organ have the same number 

 and arrangement as just described for Eo. gracihsentis. 



Eorhynchus emydis (Leidy). This form possesses a terminal 

 proboscis organ of the type described by Hamann for E. proteus 

 and E. angustatus. It is supplied with two large oval nuclei in 

 the central enlarged portion and with two small spherical nuclei 

 in a region at their posterior margin. The general relations of 

 these parts are well shown in figure 45, a copy of Hamann's figure 

 28, plate 3, representing the condition found in Eo. agihs (Rud.). 



Eorhynchus cylindratus. The terminal organ of the proboscis 

 has the same structure and arrangement of nuclei as emydis. The 

 two large oval nuclei lie side by side, while the two smaller ones 

 occur posterior to them. 



Eorhynchus tenellus. Here the organ at the end of the probos- 

 cis (fig. 38, Tpo) is of the type just described for the last two species, 

 and the constancy of the cellular elements is identical. 



5. Proboscis wall and receptacle ivall 



Eorhynchus gracihsentis. The nuclei of the walls of the pro- 

 boscis and its receptacle in this species have the following arrange- 

 ment: The anterior end of the proboscis bears a circle of twelve 

 nuclei, located in the region near the bases of the terminal hooks, 



