48 W. BALDWIN SPENCER. 



tissue, in which are both obliquely and circularly disposed 

 muscle-fibres. At no stage apparently is there present any 

 mesentery attaching the tube to the body-wall. In the mature 

 form it serves as a uterus, in which the eggs lie enclosed in 

 their shells. The tube undergoes enormous growth, coiling 

 about and occupying the whole body-cavity, in which the hook- 

 glands, alimentary canal, and ovary are pushed up against the 

 dorsal wall. The uterus, as it may now aptly be called, is 

 many times the length of the whole body, though its coils are 

 so intertwined that it is quite impossible to unravel them. 

 For the greater part of its length the walls have become ex- 

 ceedingly thin, the layer of cells on the inner surface being 

 unrecognisable ; in fact, the wall has all the appearance of a 

 layer of cuticle internally, with externally a thin sheath of 

 muscle-fibres crossing one another irregularly, and between 

 the two a thin granular layer which is probably to be regarded 

 as the remnant of the cellular layer which is well developed in 

 the younger form. 



Just before the genital opening is reached the tube suddenly 

 narrows, and its structure changes completely, in somewhat 

 the same manner as Leuckart has described in the case of 

 P. tsenioides.^ The cuticular layer becomes very thick 

 indeed. Transverse sections (fig. 45) show most internally a 

 special thin layer, with projecting portions similar to that of 

 the main portion {Cu. Vg.). Between this and the epithelial cell 

 layer lies a special cuticular development {X.) showing radial 

 lines, as if each cell had secreted a part longer than itself, all 

 the parts being fused side by side to form a thick layer 

 (•08 mm. in thickness). The cells are columnar and distinct, 

 each with a well-marked nucleus close to its inner end ( Vg. E.). 

 Externally lies a strong layer of circularly arranged muscle- 

 fibres, and outside these is connective tissue, which encloses a 

 certain number of cells similar in structure to those forming 

 the hook-gland, &c. There are no traces of anything like 

 ducts passing oflF from these cells (G/. Vg.). 



In this portion of the vagina no eggs are seen ; the muscles 

 ' Loc. cit., p. 87. 



