Anatomical structure of Aspidogaster conchicola. 483 



onto the walls of the mouth cavity, through the pharynx, and for a 

 distance into the intestine (Fig. 1). The cervico-pedal pit and the 

 genital sinus are lined with cuticle and it extends for a short space 

 into the excretory pores and so-called sense organs. 



The thickness of the cuticle varies on different parts of the body. 

 Over the ventral sucker it is much thinner than elsewhere, and in 

 various places e. g. between the edge of the sucker and the side 

 walls of the foot it levels over small depressions giving thick and 

 thin places side by side. Round the body and especially the neck it 

 may form broad circular bands, and ranging obliquely down the side 

 walls of the foot are thickened ridges. It measures in the living 

 animal about 8 /^i, in sections about 7 ,w. It always shows a thin 

 surface layer (Fig. 21 c') of denser consistence and more homogeneous 

 structure than the thick underlying layer. Voeltzkow •) calls the 

 upper layer cuticula and the lower subcuticula or matrix. In 

 examples where methylen-blue has taken effect the inner layer is inter- 

 spersed with small deeply stained dots. These are called by Zacha- 

 RiAS chromatophil-granules. Occasionally I have noticed, in living 

 animals, round the margins of the mouth and ventral sucker, bulgings 

 on the surface of the cuticle corresponding to elliptical-shaped ré- 

 fringent bodies lying in the cuticle itself. These I have taken for 

 secretion globules stopped up in the cuticle, but in the embryo I 

 have also seen similar structures which gave me the impression of 

 sensory cells. Two papillae are especially prominent on the front 

 border of the posterior sucker of the embryo. These, I am satisfied, 

 are not of the same nature for they can move sideways and with- 

 draw. Later, in post-ovic development I have noticed a row of blunt, 

 conical projections round the edge of the forwardly lengthening sucker. 

 Here and there are also to be seen openings of the skin glands 

 through the cuticle. Under abnormal conditions, more especially when 

 subjected to pressure, the cuticle develops little bladder like expansions 

 which rapidly increase in number and size till they burst through the 

 surface. When, as now and again happens in portions of sections, 

 the cuticle becomes loosened away from the underlying parts, there 

 is left intact a dense, deeply-staining line (Fig. 21 IL) bounding the 

 outer muscle-layer of the body. This is always to be seen in sections 

 and has been taken for a part of the cuticle or for a definite inter- 



1) The reference is always to that work oi an author mentioned 

 in the list. 



