55 



and they were placed in spirit of wine for the purpose of preserving 

 them previously to their being dissected. Several days after my at- 

 tention had thus been directed to the subject, I happened to observe 

 at the bottom of a jug of New-River water a small living object, which 

 appeared very much to resemble the larvae which I had recently been 

 examining ; and upon placing this under the microscope I found the 

 resemblance to be complete, except that the animal was only about 

 two-thirds the size of the former. It was deficient also in the pinnae 

 upon the lateral spines, which were simple, but the mandibular appa- 

 ratus was perfectly formed. On making further search two other in- 

 dividuals of the same species were found in different stages of growth ; 

 the smallest, however, not exceeding one-third of a line in length, 

 though still possessing some of the characters of the larger ones. 

 One of these specimens was very lively, moving freely at the bottom 

 of the water, and frequently protruding and retracting its proboscis, 

 by which it dragged itself along. 



This fact is a matter of some interest, as furnishing a clew to the 

 source of these parasites, since it is evident that the larvae can pass 

 along the water-pipes which supply the metropolis, and may thus be 

 swallowed in the water used for food : and in the present case the 

 larvae, or the ova, must have traversed a distance of at least a mile. 

 At the same time it is evident that this cannot always afford an expla- 

 nation of their mode of entrance into the body, because in the case 

 of the clergyman at Cambridge it is expressly stated that " he never 

 drank water unmixed, but generally beer, tea," and the like ; at the 

 same time the water used for these beverages was entirely supplied 

 from a pond on a stiff clay. If therefore the ova found entrance 

 with the fluid aliments, they must have withstood the action of heat, 

 as in making the beer, tea, &c. ; while on the other hand it is difficult 

 to suppose that they passed in with the solid food, because the larvae 

 are evidently aquatic. Perhaps the most inexplicable part of the 

 case is, the fact of their occurrence in such immense numbers. In 

 the Cambridge case several quarts were passed in a few months, and 

 in the instance which I have just recorded they were described as 

 coming away by handfuls. It is extremely difficult to account for 

 this fact, because a number of larvae, or their ova, must have been 

 swallowed equal to those which were evacuated, since they could not 

 multiply by generation in the alimentary canal, they being in the 

 larva state, and having, as the dissection showed, and as is well known 

 in the case of larvae, the generative organs undeveloped ; indeed no 

 trace of generative organs was visible : while it is difficult to suppose 



