272 H. J. VAN CLEAVE 



yet no direct connection could be traced between nuclei and 

 hooks. Figure 10 shows the relations of these nuclei in a cross 

 section of the proboscis. The nuclei of this group are small spheres 

 of chromatin 0.005 mm. in diameter, each lying in the center of a 

 0.007 mm. clear space. Two pairs of nuclei are connected with 

 the muscle sheath which effects the retraction of the hooks. These 

 lie, one on the dorsal side of the proboscis and one on the ventral 

 side, in the region between the second and basal rows of hooks. 

 The location of these nuclei is shown in figure 6, which is a single 

 sagittal section including but one nucleus of each of the two 

 pairs. 



The muscular wall of the proboscis receptacle proper has three 

 pairs of nuclei. The most conspicuous of these is a pair of oval 

 nuclei connected with the sheath musculature directly at the base 

 of the brain (fig. 8). The other two pairs are located, one pair 

 dorsally and the other ventrally, on the wall of the receptacle just 

 anterior to the brain. 



Eorhynchus longirostris. Due to the crowded condition of the 

 receptacle in this species, brought about by the usual partial 

 inversion of the proboscis, very little could be made out regarding 

 the cellular structure of the proboscis receptacle. The two nuclei 

 associated with the muscular wall at the base of the brain are very 

 distinct. 



Eorhjaichus emydis. The muscular wall of the proboscis re- 

 receptacle is suppUed with three pairs of oval nuclei. One pair 

 is located on the inner wall of the receptacle at the base of the 

 brain. The other two pairs are located on the inner side of the 

 dorsal and ventral walls, a short distance cephalad from the brain. 

 In the proboscis two pairs occur, one on the dorsal side of the 

 proboscis wall and the other pair on the ventral, in the region of 

 the bases of the middle row of hooks. 



Eorhynchus cyhndratus presents a nuclear constitution of the 

 proboscis and its receptacle identical with that of Eorhynchus 

 emydis. 



Eorhynchus tenellus has the same arrangement of the muscular 

 nuclei in the proboscis sheath and proboscis as the two preceding 



