30 THOS. H. MONTGOMERY, 



body epithelium but few nuclei occur, and these stain faintly; so the 

 fibres in this membrane are the still remaining fibres of cells, while 

 the central cytoplasmic mass and nucleus of the greater number of 

 these cells has disappeared — the numerous vacuoles in the basal 

 membrane representing spaces, where cells had previously been 

 situated. In the neurilemmatic layers, however, the nuclei are more 

 abundant, and stain more intensely. Finally, this tissue is especially 

 developed (quantitatively) in the anterior head region, where it pro- 

 duces not only intermuscular bundles of fibres, but also extensive 

 sheaths and sheets, around the blood vessels and the canal of the 

 cephalic sense-organ, these sheaths also producing the tubular ducts 

 of the cephalic gland (as Bürger, '90, has shown). 



2) Mesenchym tissue. Distribution and histology as in the 

 preceding species. 



3) Parenchym tissue. As in A. glutinosus. 



4) Intracapsular connective tissue of the central 

 nervous system, structurally as in A. glutinosus, but since none 

 of the cells contain pigment, only two modifications of these cells are 

 to be distinguished in virescens, corresponding to the modifications b) 

 and c) in the preceding species. 



5) An interstitial connective tissue of the body 

 epithelium is absent. 



VII. Tetrastemma vermiculum (Stimps.). 



1) Branched connective tissue cells, with dense 

 intercellular substance. As m Amjyhiporus (Fig. 13 I. /S, Mem). 



2) Mesenchym tissue is apparently wholly absent, the pre- 

 ceding tissue taking its place (Fig. 31). There is no trace, as there 

 is in Stichostemma, of a body cavity between the intestine and the 

 longitudinal muscle layer of the body wall; at least, not of a body 

 cavity filled with a fluid. 



3) Parenchym tissue is wanting in the head and oesophageal 

 regions, and is met with first in the middle region of the body. Here 

 it is a single layer of cells on the ventral surface (outside of the 

 circular musculature) of the proboscis sheath, but at the posterior 

 end of the sheath, we find the cells about three deep on the ventral 

 surface, and a single layer of cells on the lateral and dorsal surface 

 (Fig. 31 Par). As in Amphiporus, this layer is in contact with the 

 dorsal side of the dorsal blood vessel; but no parenchym cells sur- 

 round the lateral vessels, nor their commissures. Although these cells 



