200 Miscellaneous. 



layer, which places this worm among the Holomyaria. AVithiii 

 this muscular layer the cavity of the body is occupied in the centre 

 by the digestive tube, and in the interval by a spongy tissue formed 

 by intercrossed fibres, the meshes of which are filled with large, 

 round, nucleated and nucleolated cells. 



The single ovary is straight, and formed by a tube with a central 

 rhachis, to which the ova are attached laterally like the barbs of a 

 feather. The vulva opens not far from the mouth. The male 

 possesses a simple spicule ; his posterior extremity is twisted like a 

 crozier. 



The specific identity of the encysted larva and the free adult ap- 

 peared to me to be sufficiently proved by the anatomical characters ; 

 but in order to arrive at more absolute certainty, I undertook some 

 experiments in artificial migration. As I found it difficult to 

 manage the rats caught in traps, in which these migrations would 

 naturally take place, I made use of white rats {Mus raft as), which 

 I fed with cockroaches infested by these parasites. The three 

 rats experimented on were killed in a week, when I found in the 

 anfractuosities of the mucous membrane of the stomach the 

 Nematoid in question, alive and freed from its envelopes. In one 

 of the rats I found three females and a male, all of which had 

 acquired their reproductive organs. 



Thus the last period of evolution is accomplished. The copulation 

 takes place in the digestive tube of the rat ; and soon afterwards the 

 deposited ova are ejected with the fiecal matters. I do not know 

 whether these ova contain a ready-fomied embryo. However this 

 may bo, these ova are swallowed by the cockroaches, whose voracity 

 drives them to devour the excrement of the rats ; the embrj'os are 

 then hatched in the digestive tube of those Ovthoptera, pierce its 

 wall, and go to encyst themselves iu the adipose body, to wait 

 there until the Piriplaneta is in its turn eaten by the Rodent, in 

 which the evolution-cycle will be completed. A very simple obser- 

 vation also enables us to demonstrate how the migration of FUaria 

 rhytipleurites is effected. Having examined the matters contained 

 in the intestine of Periplaneta orientalis, I found there a great 

 quantity of rat's hairs. Now the rats, as indeed all the Mammalia, 

 by licking themselves, introduce into their digestive tube a consider- 

 able mass of hairs, which are got rid of with the fjecal matter. It 

 is therefore certain that the hairs which are met with in the alimen- 

 tary canal of the cockroaches have been brought there with the 

 faeces of the rat, and that the ova of the Nematoids were ingested at 

 the same time. 



Tbe observations and experiments just detailed seem to me to be 

 of some interest, as hitherto only a single case of the peregrination 

 of a Nematoid from an insect to a mammal, and vice versa, was 

 known*. — Comptes Rendus, July 8, 1878, p. 75. 



* Leuckart has discovered that Spiroptera ohtnsa, encysted in the larva 

 of Tetiebrio moUtor, completes its development in the digestive canal of 

 the mouse. 



