1901.] NATURAL SCIENCES OF PHILADELPHIA. 717 



assume a more ventral position, finally lying on the ventral surface 

 of the body, Plate XLI, i\g. 27. In this position they pass over 

 into the caudicle. In the caudicle, fig. 28, C.L.N., the nerves lie 

 latero-ventrally, and extend to the posterior end. 



The transition from the end of the body to the caudicle is also 

 marked by the sudden disappearance of the cutis and outer longi- 

 tudinal muscle layer. This is seen in fig. 27, a slightly oblique 

 cross section, that passes through the wall of the body dorsally and 

 the wall of the caudicle veutrally. 



A cross section through the caudicle, fig. 28, shows that it is 

 a hollow tube with the following structure: (1) the epithelium, 

 (2) the two lateral nerves in the epithelium, (3) the circular mus- 

 cle, (4) the inner longitudinal muscle, and (5) mesenchyme cells 

 bordering on the central blood space. 



The epithelium is composed of ciliated supporting cells, fig. 12, 

 «S'. C, very similar to those of the body, but with a smaller cell body 

 and longer stalk (cf. figs. 2 and 12) ; large gland cells, fig. 11, lying 

 mostly on the dorsal surface, the secretion staining red with eosin, 

 with very large nuclei at the base and abundant cytoplasm enclosing 

 the secretion ; and very numerous interstitial connective tissue cells 

 between the bases of the epithelial cells, above the basement 

 membrane. The epithelium of the caudicle as a whole is slightly 

 higher than that of the body, measuring about .04 mm. in height. 

 The nuclei of the connective tissue cells, fig. 28, Cii.T.N., are so 

 prominent and the cells so numerous that the effect is like that of 

 undifferentiated tissue. Biirger^- (1895), p. 239, .says in this con- 

 nection: " Es lasst der Reichthum an Kernen wohl keinen an- 

 deren Schluss zu, als dass die Zellelemente der Gewebsschichteu 

 und des Parenchyms des Scliwiinzchens im Vergleich zu denen des 

 Korpers ganz ausserordentlich klein sind." 



The lateral nerves, fig. 28, C.L.N. , lie in the epithelium outside 

 the circular muscle layer, latero-ventral in position. No ganglion 

 cells could be detected around the fibrous core. The circular muscle 

 layer, CM., is reduced to a very thin layer of two or three fibres; 

 the longitudinal muscle, i.L.M., is also a layer of but little thick- 

 ness. The central blood space, Bl.L., is bordered by scattered 

 mesenchym cells, mes., large pear-shaped cells, attached at first to 

 the muscular wall, but later floating freely in the lacuna. 



'- For the sake of clearness the great numbers of the connective tissue cells 

 in the epidermis are not represented in fig. 28. 



