CELL CONSTANCY IN THE GENUS EORHYNCHUS 273 



species. This arrangement is shown in figure "38, from which one 

 nucleus of each pair of dorsal and ventral receptacle wall nuclei 

 has been omitted in the reconstruction. 



6. Invertors of the proboscis 



Eorhynchus gracilisentis. The proboscis invertors consist of 

 two strips of tissue which extend backward along the dorsal 

 and ventral surfaces of the terminal proboscis organ and pass 

 through the base of the proboscis sheath. In the region anterior 

 to the brain each invertor bears a pair of elongated or spindle 

 shaped nuclei. In this species the invertors are so highly devel- 

 oped that they almost entirely fill the space within the walls of 

 the proboscis and its sheath. 



Eorhynchus longirostris. In this species the same structures 

 are found. The invertors are somewhat reduced in size so that 

 they stand out more clearly as separate structures. As in the 

 preceding case each of them is supplied with two nuclei. Figure 26 

 shows these invertors cut in a slightly diagonal plane so that but 

 a single nucleus shows in each. 



Eorhynchus emydis. Figure 44 is a drawing from a toto 

 mount showing the pair of nuclei associated with each invertor. 



Eorhynchus cylindratus. The nuclei in the invertors are iden- 

 tical with those found in Eo. emydis. The invertors are in about 

 the same stage of development. 



Eorhynchus tenellus presents the same distribution of one pair 

 of nuclei to each invertor, as shown in figure 38. 



7. Retractors of the proboscis receptacle 



In the genus Eorhynchus the retraction of the proboscis re- 

 ceptacle is accomplished through the contraction of two long 

 fibrous bands which proceed from the posterior end of the pro- 

 boscis receptacle and find attachment, one on the dorsal wall of 

 the body and the other on the ventral body-wall. These retrac- 

 tors are direct continuations of the proboscis invertors. 



Eorhynchus gracilisentis. The dorsal retractor of the proboscis 

 receptacle in this species is supplied with two oval or spindle 



