378 ENTOZOA. 



ing in a certain pond whose muddy sediment swarmed with micro- 

 scopic tank-worm (Urohales palustris, Carter), twenty-one were 

 attacked with Dracunculus during the year, whilst the boys of other 

 schools, bathing elsewhere in the island, were not infected with the 

 exception of one or two individual instances here and there. This 

 remarkable occurrence also points to the possibility of the young 

 Dracunculi being occasionally confined to particular pools of water, 

 or, at least, to the probability of their being much more abundant 

 in some waters than others, although the whole locality may be 

 harbouring them in greater or less abundance. Such a distribution 

 is in unison with the general law affecting the variable prevalence of 

 other animals in particular localities. A great deal has been writ- 

 ten respecting the nature of the soil and other geological characters 

 occurring in the Indian worm-districts ; but the speculative views 

 enunciated in reference to their connection with the prevalence of 

 Dracunculus are, to my mind, little worthy of credit. However, 

 those who think otherwise should consult the writings of Smyttan, 

 Greenhow, Bird, Chisholm, Forbes, and others ; and especially, also, 

 the admirable resume given by Aitken in the last edition of his 

 work on " The Science and Practice of Medicine." 



Structure. — If a full-grown Dracunculus medinensis be re- 

 moved from the subcutaneous cellular tissue in its entirety, it 

 is invariably found to exhibit the aspect of a uniform cylindrical 

 worm, whose anterior and posterior extremities are only distin- 

 guishable from one another by the circumstance that the former is 

 somewhat bluntly rounded off, whilst the latter is suddenly attenu- 

 ated so as to form a short, filamentary caudal appendage. This 

 so-called tail is most commonly curved and retroverted, but it is occa- 

 sionally straight, under which condition it bears some resemblance 

 to the terminal intromittent organ of a male Strongylus. I believe 

 it was the occurrence of this rather unusual peculiarity in the cau- 

 dal formation which led Owen to believe that he had stumbled upon 

 a male Dracunculus, and which further induced him to figure the 

 same in his well-known article " Entozoa" in " Todd's Cyclopedia." 



