: OF THE NEMATOIDS, PAEASITIC AND FEEE. 609 



at a distance of ^5-" from the posterior extremity of the body two large caudal pores, 

 apparently homologous with what are also seen to exist in the caudal regions of the 

 Ascandes and so many other Nematoids (Plate XXVII. figs. 20, c & 21). And what I 

 have described in the young of this animal as " lateral sacculi," I now suspect may be 

 the early representatives of these lateral pores in the adult. The protrusions which are 

 seen to exist in the place of these sacculi in some individuals are, I believe, due to a 

 complete or partial extroversion of the walls of the sacculi. The proportionate size of 

 these structures, as existing in the young, is certainly very large as compared with the 

 pores in the adult ; but if the sacculi are not to be considered their representatives, then 

 we must look upon them as bodies altogether anomalous ; whilst if they are so con- 

 sidered, we may expect to find the same structures more or less developed in the young 

 of many other Nematoids. The differences in the relative position of anus, pores, and 

 posterior extremity, as met with in young and old specimens of Dracuncubis, is nothing 

 more than might be expected, considering the enormous dc\elopment attained by the 

 adult, and tlie obviously wasted condition m it of the very elongated filiform posterior 

 extremity existing in the young animal. 



As I have stated elsewhere*, I am strongly inclined to believe that the Guineaworra 

 was originally a free Nematoid, which, having obtained a dii'ect entrance into the human 

 body through the skin, attains an enoimous size in the subcutaneous tissue. In the same 

 place I pointed out, however, reasons why it could not, as Carter imagmed, be identical 

 witli his Urolahes iMlustris. The principal anatomical reasons lending support to the 

 view of its being an enormously developed free Nematoid, are the following : — it has a 

 very wide lateral intermuscular space, but no development whatever answering to the 

 lateral band (Plate XXV. fig. 14,/"), and, so far as we at present know, this is the case with 

 no other parasitic species, though it is by no means uncommon amongst the free Nema- 

 toids for all traces of these structures to be absentf ; the form of the young Guinea- 

 worms with their attenuated filiform extremities agrees closely enough with what is of 

 most common occurrence amongst the free species, whilst if it exists at all amongst the 

 parasitic forms, it must be a matter of the greatest rarity, since the only recorded 

 instance of any approach to such a length and tenuity of the body posterior to the anus 

 that I am aware of is in Passalurus amhiguusX ; and finally, so far as yet ascertained, the 

 symmetrical condition of the genital organs, combined with the extreme shortness of the 

 ovarian tubes, is a condition which, so far as I am aware, can only be paralleled amongst 

 the JnguiUulidce. After further careful search I have still failed to find any trace of 

 vulva or vagina, and am moreover still inclined to believe, for the vai"ious reasons stated 

 in my memoir on this animal §, that a resort to the method of agamogenesis to account 

 for the production of its countless young, is not only most in accordance with what we 

 know of the history of this animal wliilst in the human body, but also most consistent 

 with the fact of the existence of young in the genital tube in all stages of growth, from 



** Trans, of Linn. Soc. vol. xxv. p. 12C. f O"*) »t ^ events, unreeognizable. 



X Oxyuris ambii/iia of KiTDOLPni. § Trans, of Linu. Soc. vol. xxiv. p. 126. 



MDCCCLXVI. 4 P 



