98 THE ORIGIN OF PAKASITES. 



trace of similarity to their predecessors ; they hve for several 

 months, during which time they produce a countless number of 

 eggs, which are hatched while yet in the uterus, and afterwards 

 pass ' into the intestine of their host. During their stay in the 

 intestine the emlDryos escape from the shell; they again become 

 small perfect Ehabditidse (Fig. 62), and remain in this form in the 

 cloaca, unaltered, until they are expelled with the excrement, when, 

 if surrounded by putrescent matters, they complete their life-cycle 

 in a few days. The remarkable circumstance that the parasitic 

 Rhabdonenia nigrovenosum is always found only in the female form, at 

 first led me to suppose that they propagate their species by parthe- 

 nogenesis ; but I have since found — as also Bischoff had previously 

 done — that in several individuals there were seminal corpuscles in the 

 posterior portion of the ovary among the eggs ; so that I am now 

 prepared, with Schneider and Claus, to regard this form as a herma- 

 phrodite, wlrich, as is also known to be the case in certain instances of 

 free-living Ehabditidge,^ produces seminal corpuscles in sexual organs 

 of otherwise female structure for some time before the ova make their 

 appearance. But I must add, that in many cases I have sought in 

 vain for these seminal corpuscles ; and other helminthologists have 

 also experienced the same difficulty — e.g., von Siebold — so that the 

 sibility of a parthenogenetic development is not yet entirely excluded. 

 [It was to be expected a priori that Ehabdonema nigrovenosum 

 could not be the only Nematode possessing so peculiar a life-history ; 

 but the statement of Ercolani^ as to the descent of the A. inflexa 

 and A. vesimlaris of hens from certain free-living Hhabditis-ioiiRS, 

 has no foundation in fact. On the contrary, my recent researches^ 

 lead to the conclusion that the so-called Angtiillula stercoralis (an 

 unmistakeable Bliabditis found in the excreta of patients suffering 

 from diarrhoea in warm countries, and especially Cochin-China) pro- 

 duces sexually a new generation, which becomes transformed in the 

 intestine into the so-called A. intestinalis, represented, like Bhahdo- 

 nema nigrovenosum, only by female individuals. The same is true of 

 a sausage-shaped anenteric Nematode (AUanionema tnirdbile, Leuck- 

 art*), which is parasitic in the body-cavity of Hylohius pini, and con- 



1 See Schneider, " Monogr. d. Nematoden," p. 313; and Vernet, Arch. Scl Phys 

 Nat., t. xlv., p. 61, 1872. 



- Ercolani, "Sulla dimorphobiosi, &o.," il/c;n. .4m,(7. i?ofo(7na, t. iv., p. 237 1874 and 

 t. v., p. 391, 1875 ; Abstr. Journ. de Zool., t. iii., p. 67, t. iv., p. 254. 



•■' Leuckart, " Ueber d. Lebensgesch. d. sog. Anguillula stercoralis, u. deren Bezieh. 

 zu d. sog. A. intestinalis," Berkht d. math. phys. 01. k. Sachs. Gesellsch Wiss pp 

 75-107, 1882. 



* Leuckart, "Ueber eineu neuen heterogenen Nematoden," Sericht d. Versanml. 

 deutsch. Naturf. Maydehurg, p. 320, 1884 ; a more detailed account will shortly appear in 

 ■ Bericht. d. math. phys. CL h. Sci^'hs. Gesellsch. d. Wiss. 



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