53 
prolonged, I have had rich opportunities to observe during my 
journeys in the Pacific. 
Summarizing, one would say that the increase in size and 
specialization, as well as the changed location of the sucker, is 
considered as an accommodation to the new modus of living ac- 
quired by this Polyclad through its stay with Pagurids. 
Digestive apparatus: This resembles in the main that 
described by Lang for Prosthiostomum siphunculus. From the mouth 
a narrow tube runs upwards and backwards and with a wide free 
brim enters the foremost part of the pharyngeal pocket. The pha- 
ryngeal pocket is of considerable size, reaching dorsally and ventrally 
almost to the muscular wall of the body, separated from it only 
by very insignificant parenchymatous tissue (Plate II a, Fig. 3). It 
is further noticeable that inner longitudinal muscular fibres of the 
ventral muscle wall of the body are practically lacking in the pha¬ 
ryngeal zone. The pharynx has the organization typical for Pros- 
thiostomids, but connects with a special lip-development with the 
spacious and wide main gut which is situated exclusively back of 
it. This kind of diaphragm can be observed on Plate II a, Figs. 3 and 4. 
The main gut reaches caudally even as far as the sucker. The 
intestinal epithelium is remarkably low, and contains, as in the case 
of all Prosthiostomids, masses of Minot’s granular giand cells. 
These agree very well with those shown on the figure that Lang 
has given of Pr. siphunculus. The outer bulging part of the giand 
cell is developed as a secretory cup, while the basal half of the 
cell is narrow and filled with a compact, homogeneous-looking 
plasma stained deeply with hematoxylin. In the lumen of the 
main gut.is a coagulation of partly digested nutriment as well as 
secretion from Minot’s granular giand cells The series of sections 
show clearly that the digestive process is begun here; thus the 
partly digested liquid mass of food-matter can later be distributed 
to the intestinal coeca in spite of their narrow lumen. The thick 
epithelium of the intestinal diverticula differs greatly from that of 
the main gut. The cells form a veritable syncytium, and as is 
clearly visible in the sections, this is packed with nutritive substance; 
hence we have here a typical picture of intracellular digestion at 
Work. Large round balis of a mass stained with eosin indicate 
the presence of albuminous elements, which, together with the 
