494 JOSEPH STAFFORD, 



cross wall, so-called sense organs (Fig. 13, 6 SO). In a horizontal, 

 surface section (Fig. 14), where only the ventrally extended longitudinal 

 and transverse ridges or walls are sectioned , these two series of 

 muscles take on a radial appearance with relation to each alveolus. 

 In each alveolus lie, between the muscle fibres and aggregated into 

 a group immediately under the limiting membrane, numerous deeply- 

 staining nuclei (Fig. 4, 5, 6 K) with dispersed chromatin granules. 

 Below these and in some cases partly mixed with them are other 

 nuclei (Fig. 4, 5, 6 PN) with a single sphere (nucleolus). In sections 

 where those in the sucker can be compared with those just outside 

 the sucker, under the cuticle of the infraseptal body walls, it is seen 

 that the former are generally smaller than the latter although examples 

 can be found that are identical. The difference is no doubt due to 

 the frequent division of the nuclei in the sucker during its rapid 

 forward growth. The staining and chromatin also point to the same 

 conclusion. Here, as among the subcuticular cells, are two kinds of 

 nuclei but here the smaller nuclei are generally vastly the more 

 numerous, while under the integument the small nuclei can be easily 

 overlooked being crowded in among more prominent elements. 



In places where the chromatophile cells are less numerous real 

 cell-walls can be seen — the small cells to which they belong lying 

 between the vertical muscles of the sucker. Leuckart finds these 

 cells also in Dist. pulmonale (Menschl. Parasiten, Lief. 4, p. 415, 

 chromatophile Kernzellen). Monticelli finds similar cells in Cotylo- 

 gaster, a very close relative of Aspidogaster, and takes them for 

 cutaneous glands (glandole cutanée). 



In sections of the two middle rows of alveoli may be found, 

 instead of a collection of chromatophile nuclei, a part or almost the 

 whole of an alveolus taken up with large cells that in general appear- 

 ance, stain, and structure resemble unicellular glands (Fig. 2, 5 SG). 

 I shall have to deal with these more fully under the heading "Glands". 



Lengthways, through the marginal alveoli, slightly inwards from 

 their centres, runs a nerve (Fig. 4 N) which is continuous in front 

 into its mate of the opposite side. From this outwards extends a 

 branch to each sense organ. I mention this here simply to give, so 

 far as I know, the complete anatomy of the sucker. 



Digestive system. 



Mouth funnel. A mouth sucker as a specialized organ, 

 distinctly limited from the adjacent parts as is the ventral sucker, is 



