152 DK. H. LYSTEE JAMESON ON THE [Mar. 4, 



the cuticle, a deeper longitudinal layer (Lm.), and, on the ventral 

 surface, a less defined tract of transverse fibres inside the longi- 

 tudinal muscular coat. 



The suckers are lodged in a slight involution of the cuticle 

 (PI. XV. figs. 5, 7). Their relative and absolute sizes in surface 

 view are determined by the degree of contraction of their con- 

 stituent fibres. The venti-al sucker is about one-fourth or one- 

 thii-d of the total breadth of the body. 



The mouth is situated in the middle of the anterior sucker, 

 and generally appears triangular in sections (PL XY. figs. 6, 7, m.). 

 The funnel-shaped buccal tube opens behind, by a narrow orifice, 

 into the spherical muscular pharynx (ph.). This is followed by 

 the short straight oesophagus (os.), which, passing upwards and 

 backwards, bifurcates to form the sac-like digestive cfeca (PI. XIY. 

 fig. 2 ; PI. XY. figs. 5-7, dig.), which are dorsal to the other organs. 

 In the resting worm these cfeca are greatly distended with 

 yellowish granular material, doubtless derived from the tissues of 

 Mytilus. 



Even the oesophagus is often tightly crammed with food. 

 The digestive system in this condition occupies the bulk of the 

 body, anterior to the ventral sucker, but when empty is much 

 smaller. The posteiior end of the pharynx is provided with a 

 group of salivary glands (PI. XY. figs. 6, 7, s.gl.). The epithelium 

 of the digestive system consists of very large flat polygonal cells 

 with conspicuous nuclei (PI. XY. fig. 7, int.ep.). The individual 

 cells can sometimes be distinguished in pressure preparations. 

 There is an ill- defined supra-pharyngeal nerve commissure (PI. XY. 

 fig. 7, n.G.) and a pair of lateral cords. The excretory system 

 (PI. XIY. fig. 2 ; PI. XY. figs. 5-7, ex.) consists of two enormous 

 tubular sacs, extending to the anterior end of the body and 

 converging to form a pyrifoi-m median vesicle, which opens by 

 a pore at the hinder end (PI. XY. fig. 6, ex.p.). The excretory 

 tubes are genei-ally quite full of opaque spherical granules, 

 presvimably of excretory matter. When treated with hydro- 

 chloric acid they become transparent (PI. XY. fig. 6). 



In living specimens a few flame-cells can be seen in short, 

 lateral, and apparently unbranched tubules given oflT by the 

 exci'etory sacs. But the distended condition of the latter makes 

 it difficult to ascertain their precise relations. 



The female organs are not developed in the resting larva. 

 The worm is protandrous, and the male genital organs reach a 

 conspicuous size, even in the Sporocyst. The rudiments of the 

 testes, vasa defei'entia, and penis are very obvious in sections 

 (PI. XY. figs. 5, 7) and in stained preparations of the entire 

 worm (PI. XY. fig. 6). Being composed of young cells they stain 

 deeply. In fresh specimens they are less obvious. The penis 

 opens out at the genital pore (PL XY. fig. 7, g.p.), which is 

 situated immediately in front of the anterior border of the 

 ventral sucker. It is an elongated hollow pyriform body, lying 

 in front of and dorsal to the sucker. The rudiment of the 



