108 On the Worm which infests the Stickleback.  [Fen. 
breadth as the rest of the body, until the rings suddenly contracted 
toapoint. They were still alive, and one of the largest, which had 
been left nearest to the dead fish at the time they were examined in 
the morning, had again before evening partially insinuated its head 
into the aperture from whence it had originally escaped. 
Having expressed a desire to examine the general state of the 
sticklebacks then at large in the same pond from which the others 
had been taken, a servant was dispatched, who soon returned with 
several of them in a vessel of water. On examination, these were 
all found to be in the diseased state, all of them presenting the 
same uncouth, fiddle-shaped, appearance. They were all affected 
too in some degree by the same sort of globular pustules which 
have just been described as remarked on the dead one. Each fish 
had from one to three or four of these pustules, some of them on 
the body of the animal in different situations, and many of them 
were noticed on the fins, and even on the delicately webbed extremi- 
ties of these members. The figure above referred to is a just, though 
rude, representation of one of the most tumid of these fish, and 
three of the little pustules in question may be observed distinetly 
marked on it. Having put one of these fish to death by decapita- 
tion, I proceeded to dissect it with a pair of fine pointed scissars, 
beginning at the anus, and cutting upwards through the bony car- 
tilage of which the belly of the gasterosteus is composed. On 
laying open the cavity of the abdomen, the teeniz were immediately 
discovered, not in the intestines, but immediately beneath the peri- 
toneum. The whole cavity was so stuffed with these worms, that 
as the fish lay on its back, the alimentary canal and all the other 
intestines were completely covered and hid by them. The tieniz 
appeared to lie with their heads towards one another in the centre, 
and having their other extremities folded or rolled up in the ante- 
rior and posterior regions of the cavity, so as to form the double 
protuberance so distinctly visible in the external appearance of the 
fish when alive. The tenis, which were above an inch in length, 
and four in number, were perfectly lively when removed from their 
situation. One of the globular pustules figured in the sketch was 
now subjected to minute dissection under the microscope, when it 
was found to be merely a diseased sack, formed by a distension of 
the skin of the fish, of the colour and spots of which it partook 
according to its situation on the body of the animal; having the 
neck which attached it to the rest of the skin extremely slender. 
When opened, it was found to contain a whitish coloured, and 
rather viscid, pus. It is probable that these pustules were merely 
attendant symptoms of the diseased state of the sticklebacks. 
It would seem from the circumstances just detailed that as soon 
as the gasterosteus aculeatus has provided for the continuation of its 
kind, by depositing or impregnating its ova, it is immediately 
doomed to a gradual destruction by the tenia solida, with which it 
then begins to be internally infested. And if this fact be esta- 
blished, and the connexion between the time of spawning and that 
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