52 
in addition thick bundles of dorso-ventral muscular fibres. A con- 
siderable number of secretory duets from the surrounding body- 
section traverses the thick stem on their way to the adhesive disc. 
The secretion is very fine-granular and erythrophile, and is formed 
in giand cells situated in the parenchyma, but only ventrally 
to the intestinal coeca. The abundance of secretion that is taken 
to the adhesive disc shows what an important role it plays in the 
funetion of the sucker. 
The great size of the sucker deserves special notice. If one, 
in order to get a good measurement for comparison, uses the 
relations between the size of the sucker and that of the brain, the 
two are found, in the case of Prosthiostomum, to be of about the 
same size. But in Euprosthiostomum the length of the sucker exceeds 
the greatest diameter of the brain many times. On account of the 
great contractibility of the body, I do not consider the relation, 
length of sucker: length of body very practical for comparative 
purposes. That follows indireetly from the remarks on page 50. 
I have no doubt but that the splendid development of the sucker 
must be connected with the peculiar habits of the animal, being 
an adaptation for the life as intruder. I only wish to remind the 
reader of the Bdelloura species inhabiting Limulus. Their sucker 
is quite a new acquirement, as the free-living Tricladida maricola 
are devoid of such an organ. As a Colylean Polyclad Euprosthi¬ 
ostomum possessed a sucker already before taking up its stay in 
the houses of the Hermit crabs. The displacement of the sucker 
to the posterior end of the body I am also inelined to regard as a 
result of altered living conditions and as of direct value for the 
animal. The genus Bdelloura just mentioned, as well as ectoparasitic 
Trematods, have a sucker, and suckers respectively, located at the 
hinder end of the body. Thus, in this Prosthiostomid, while the sucker 
retains its hold to the substratum, the area for collection of food is 
inereased, in comparison with other members of the family, where 
it is subcentrally located. It might further be pointed out that the 
feeding range is inereased to a considerable degree through its 
possession of a tubular pharynx, which undoubtedly can be pro- 
truded and prolonged in the way characteristic of other Prosthio- 
stomids. How efficient this organ is in Prosthiostomum in obtaining food, 
how excellent it works as pump mechanism, and how far it can be 
