88 The Sunfish as a Host. 



sheathmg-tubes, the orifices of the latter being closed by four 

 papillasform elevations, symmetrically disposed near the centre. 

 It will also be further seen that the sucking disks coalesce on 

 either side, so that the four cephalic lobes are rather to be re- 

 garded as two auriculate appendages, deeply cleft transversely 

 in the middle line. In form they strangely resemble, as it 

 were, a pair of cloven hoofs placed heel to heel. The four pro- 

 boscides are club-shaped, each being furnished with a compli- 

 cated armature of hooks, arranged in circular rows. The latter, 

 though scarcely visible to the naked eye, present a formidable 

 appearance when magnified. This is shown in fig. 5, where 

 one of them is enlarged twenty diameters. Very difficult was 

 it found to ascertain the precise number of hooks, but after 

 careful and oft-repeated examinations, we satisfied ourselves 

 that each circle consisted of sixteen hooks (fig. 6), whilst there 

 appeared to be fully one hundred of these rows on each pro- 

 boscis. Each tentaculum, therefore, was calculated to carry 

 about 1600 hooks, which would give us altogether a total of 

 more than 6000 of these little instruments on a single tape- 

 worm. The majority of the hooks displayed a tolerably uni- 

 form length and thickness when compared with each other, 

 but the two lowermost circles near the base of each proboscis 

 were two or three times the size of any of the others. Fig, 7 

 represents one of the large hooks, with its somewhat blunted 

 extremity directed obliquely downwards ; and fig. 8 shows one 

 of the numerous small hooks having the end more curved, 

 pointed, and retroverted. Both these figures are from hooks 

 magnified about 250 diameters. The body of the Tetrarhyn- 

 chus is distinctly segmented; the joints gradually acquiring 

 greater conspicuity the further we recede from the so-called 

 head. This character is partly exhibited in the lower half of 

 fig. 3, but a few well-marked articulations from the posterior 

 region of the body are faithfully illustrated at fig. 4. Lastly, 

 it is particularly worthy of remark, that none of the segments 

 display the slightest indication of the presence of reproductive 

 organs, such as we should undoubtedly have discovered if the 

 tapeworm or its joints had been fully developed and matured. 

 The explanation of this will appear in the sequel. 



Reverting to the questions previously mooted, we may 

 observe, that the object of the tunnelling process appears to be 

 two-fold : first, in order that the animal may constantly obtain 

 fresh nutriment, and secondly, because the creature is impelled 

 by instinct to seek out another " residence," which it can only 

 gain by being transferred to a separate " host." The tapeworm 

 not being supplied with any mouth or digestive organs, ac- 

 quires nutriment by imbibition through the general surface of 

 the body ; and the reason why it needs transference to another 



