458 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



characters which seem, on the whole, to stand intermediate between 



The lacunar system of Pandosentis is especially conspicuous in 

 many individuals ; in fact, the distances between the annular lacunae 

 in the body wall are frequently little more than the diameter of a 

 single lacuna (fig. 7). The body wall is only about 50a in thickness. 

 This gives to the individuals a distinctly fragile appearance. The 

 nuclei of the subcuticula are of the type previously described for 

 Gracilisentis. The unusual irregular distribution of the dorsal sub- 

 cuticular nuclei mentioned in the generic diagnosis is associated with 

 the fact that the lacunar system is not absolutely regular in its 

 arrangement of parts. In some portions of the body there are dis- 

 tinctly dorsal and ventral main canals with regular annular inter- 

 communications between them. This is especially typical of the an- 

 terior region of the body. Figure 7 represents a portion of the dor- 

 sal lacuna and its lateral branches from the anterior extremity of 

 the body. In other regions of the body (fig. 8) this definiteness of 

 arrangement is replaced by irregular diagonal canals communicat- 

 ing with the annular lacunae. The giant nuclei of the subcuticula 

 have definite relationships to the lacunar system. In most of the 

 Neoechinorhynchidae the longitudinal trunks of this system are dis- 

 tinctly dorsal and ventral in location. In all such cases which have 

 been observed by the writer, the giant nuclei are all located in the 

 sagittal plane of the body. In Pandosentis the irregularity of the 

 longitudinal trunks of the lacunar system is directly associated with 

 an irregularity in arrangement of the subcuticular nuclei. Figure 8 

 shows one of the giant nuclei from the posterior extremity of a ma- 

 ture male. The irregularity of the lacunar system in this region is 

 readily observable. 



In working out the morphology of this species nearly 100 speci- 

 mens were studied. Of these only three or four had the proboscis 

 sufficiently protruded to make a study of the hooks and their arrange- 

 ment possible. Inversion of the proboscis is due to the action of the 

 strongly developed invertor of the proboscis, which, in this species, 

 is one of the most conspicuous structures in the anterior region of 

 the body. It is conspicuous even in toto mounts, and in the extended 

 proboscis occupies much of the interior of that organ. There are 

 three conspicuously large nuclei in this invortor muscle (fig. 5). 



