TETRAEHYNCHIDJl. 139 



quadrilateral figure, with the angles rounded off, each lateral half 

 being furnished with a bipartite facet, which, in form, presents a 

 remarkable resemblance to the under surface of a cloven foot 

 with the digits pointing outwards. The four bothria thus appear 

 to merge into one another towards the centre of the head, near 

 which point the openings of the four proboscis- sacs are brought into 

 view. The retractile boring-organs are club-shaped, each being 

 furnished with an armature of hooks, differing in many respects 

 from those I have previously described. It was difficult to ascertain 

 their number precisely, but after careful and oft-repeated examina- 

 tions, I arrived at the conclusion that each circular row consisted of 

 sixteen hooks (Fig. 6), whilst there appeared to be fully one hundred 

 of these rows on each proboscis. Each proboscis was therefore 

 calculated to support 1600 hooks ; which therefore gave, altogether, 

 a total of upwards of 6000 of these little instruments on a single 

 head. Nearly all the hooks displayed a uniform length and thick- 

 ness, but at the lower part of each proboscis there were two con- 

 spicuous circles, the hooks of which were at least twice as large as 

 the others (Figs. 7 and 8). The smaller hooks are curved, retro- 

 verted, and sharply pointed at their tips ; the larger ones being- 

 less arcuate, less retroverted, and comparatively blunt at their 

 extremities. Finally, in regard to the neck and body, it only 

 remains for me to add that the former is, in the first instance, con- 

 tinuous with the head, subsequently becoming enlarged, and then 

 afterwards contracting, as suddenly, before it re-enlarges to form 

 the upper part of the body. At this point braces of segmentation 

 commence, becoming more and more evident as we pass down- 

 wards, until the joints are well formed ; and these latter, but 

 for the absence of sexual organs, would probably not be distin- 

 guishable from the proglottides of the adult strobila. 



Several questions here naturally suggest themselves, such as, — 

 What is the object of this perpetual tunnelhng ? Does the boring- 

 cause suff'ering to the host ? Do the parasites ever make their 

 escape from the body of the fish, by their own unassisted powers ? 



