TWO SPECIKS OF CVSTICERC'OIDS. 1 ."{ 



20 to 24 spines. Llilie, to wliom tlie specimen was refevi'ed, 

 mentioned the supposition tliat the Cysticercoid might be that of 

 Ilyinenolepis nana (v. vSieb.). 



From the description given of the second Cysticercoid it was 

 apparent that it was very like the scolex of Hymenolepis mur-ina 

 I)uj., a freqnent parasite of vaiious species of rats. Tlie size of 

 the scolex of the Cysticercoid, the arrangement, number, size, and 

 shape of the spines all agreed with those of Hymenolepis murina, 

 and it was certainly the only rat-tapeworm to which the Cysti- 

 cercoid could be referred. Tlie closely allied Hymenolepis iniet'o- 

 stoma Duj. had 30 spines of much smaller size, //. contracta 

 Janicki and H. maris variegati Janicki, neither of which corre- 

 sponded to the Cysticercoid, were the only other ai-med Hymeno- 

 lepids found in rats, ami the authors were forced to the conclusion 

 that this C3^sticercoid must either be I'eferred to H. 7nurina or 

 to some other as yet vmdescribed form, the scolex of which was 

 indistinguishable from that of H. mu?-ina. 



Hitherto the life-history of H, viurina had been believed to be 

 of a unique type. According to the researches of Grassi and 

 Rovelli {op. cit. pp. 75-83) this tapeworm dispensed altogether 

 with an intermediate host, and they had demonstrated that it 

 passed its encysted stage in the walls of the intestine of the rat 

 itself. This was supported on general gi-ounds by the fact that 

 this particular tapeworm usually occuired in enormous numbeivs, 

 which would involve the ingestion of a correspondingly large 

 number of intermediate hosts. The matter gained interest from 

 the fact that H. murina was believed by some to be identical with 

 H. nana, a dangerous tapeworm of man, although the identity was 

 still a matter of dispute. In size and structure the two species 

 w^re indistinguishable, and H. nana like //. mnrina occiu-red in 

 enormous numbers. Further, no intermediate host had yet been 

 discovered for H. nana. Now the discoveiy in the rat-flea of this 

 Cysticercoid bearing such a close resemblance to the scolex of 

 H. 'murina led to one of two conclusions : either that, as already 

 mentioned, there might be some undescribed tapeworm of which 

 the Cysticercoid was the larval stage, or that the rat-flea might 

 function as an intermediate host of H. murina. The latter 

 supposition, even if coirect, did not necessarily disprove Grassi and 

 Rovelli's results. Rats certainly ingested a large number of fleas 

 from time to time, but it was difficult to imagine that they would 

 acquire a very large infection with H. mu7^ina by this means ; 

 and if H. nana be identical with H. murina it was scarcely 

 conceivable that a human being could accidentally swallow a 

 sufficient number of fleas to give rise to an infection of over a 

 thousand tapeworms, as was frequently found to be the case. It 

 would still therefore be necessary to admit that the development 

 of H. marrna usually took place without an intermediate host, 

 but that occasionall}^ the rat-flea might function as such. With 

 such a conclusion the life-history of H. murina became even 

 more remarkable than before. 



