NEMATODA 219 



conveyed in water is also further indicated by the well-known 

 fact that in India, where it is the custom of the natives to carry 

 water in skins on their backs, the worm makes its appearance 

 on the back and shoulders and upper part of the body/' 

 These views were published by Bask in 1846, and I am free to 

 confess that confirmed as they appeared to be by subsequent 

 and independent testimony they completely dominated my con- 

 ceptions as to the mode of ingress of the young parasites within 

 the human bearer. Thus, those of our Indian troops which 

 were most exposed during the rainy season, subsequently 

 exhibited evidence of having been invaded by the Dracunculus. 

 As, moreover, the period of incubation of the entozoon com- 

 monly extends from twelve to fifteen months, it necessarily 

 happened that the disease often showed itself in localities far 

 distant from the spot where the troops originally contracted the 

 disorder. The statement that the period of incubation of the 

 worm is not less than a year, is probably incorrect, since Carter 

 mentions that in a school of fifty boys bathing in a certain pond 

 at Bombay the sediment of which swarmed with microscopic 

 tank-worms (Urobales palustris, Carter)- twenty-one were 

 attacked with Dracunculus during the year, whilst the boys of 

 other schools, bathing elsewhere, remained, with few exceptions, 

 uninfected. This is a remarkable occurrence, and it points to 

 the possibility of the young Dracunculi being confined to 

 particular pools. That they should, whether occupying the 

 bodies of intermediary bearers or not, be more abundant in some 

 waters than others, is just what might be expected, since such 

 a distribution is in harmony with a recognised law affecting the 

 abundance or limitation of species in particular localities. 

 Much, indeed, has been written respecting the nature of the soil 

 and geological formations occurring in the Indian worm- 

 districts, but the speculative views enunciated on this point are 

 little worthy of credit. Those who desire information on this 

 head should at all events consult the valuable writings of 

 Smyttan, Greenhow, Bird, Forbes, Chisholm, and Aitken, 

 who, apart from the question at issue, supply abundance of 

 practical information. 



Into the anatomy of the adult Dracunculus I do not enter, 

 but I may remark in passing, that the structure of the worm 

 has been exhaustively treated of by Busk and Bastian. A 

 resume of their views is given in my introductory treatise. Carter 

 and Leuckart have also added important details. As regards 



