98 THE ORIGIN OF PARASITES. 



trace of similarity to their predecessors; they live 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 embryos escape from the shell; they again become 

 small perfect Ehabditidae (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 

 Rhabdonema 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 Glaus, to regard this form as a herma- 

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

 free-living Ehabditidse, 1 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 Rhabdonema nigrovenosum 

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

 but the statement of Ercolani 2 as to the descent of the A. inflexa 

 and A. vesicularis of hens from certain free-living Rhabditis- forms, 

 has no foundation in fact. On the contrary, my recent researches 3 

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

 unmistakeable Rhabditis 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 Rkabdo- 

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

 a sausage-shaped anenteric Nematode (Allantonema mirabile, Leuck- 

 art 4 ), which is parasitic in the body-cavity of Hyldbius pini, and con- 



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

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



2 Ercolani, " Sulla dimorphobiosi, &c.," Mem. Accad. Bologna, t. iv., p. 237, 1874, and 

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



3 Leuckart, " Ueber d. Lebensgesch. d. sog. Anguillula stercoralis, u. deren Bezieh. 

 zu d. sog. A. intestinalis," Bericht d. math. phys. Cl. Tc. Sachs. Gesellsch. Wiss., pp. 

 75-107, 1882. 



4 Leuckart, "Ueber einen neuen heterogenen Nematoden," Bericht d. Versamml. 

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

 Bericht. d. math. phys. Cl. k. Sachs. Gesellsch. d. Wiss. 



