Some Variations in Hymenolepis dimimita 5 



Of the hosts examined for sex forty-two were males and 

 twenty-six were females. This difference probably represents a 

 greater number of males present in nature rather than any special 

 factor which leads the female to avoid traps. All sizes, all places, 

 and all months were about proportionately represented in both 

 sexes. Males and females were about equally infected with ces- 

 todes. But one cysticercus was found among the males as com- 

 pared with four among the females. Both sexes were infected 

 frequently with ectoparasites, with nematodes in the bladder and 

 with trypanosomes in the blood. With regard to the last the 

 males showed eight cases of infection, the females two. 



The size of the host does not seem to be a very important fac- 

 tor except with regard to infection of the blood with trypanosomes 

 and nematodes in the bladder. The full-grown rats came from a 

 great variety of places, and were caught during all the months. 

 The same is true of the smaller animals. Size is independent of 

 sex also. Nematodes in the bladder are rather characteristic of 

 the full-grown and trypanosomes in the blood of the half-grown 

 rats. Of the full-grown animals 73 per cent are infected with 

 cestodes as compared with 61.5 per cent of those half-grown. 

 As a rule a smaller number of worms is found in a cestode infec- 

 tion of a full-grown rat. 11.9 on the average, than of a half-grown 

 specimen, averaging 27.8. 



The effect of place where the rat was captured had very little 

 to do with the infection by parasites. It has apparently no effect 

 on size or sex of the animals. Eleven of the thirteen cases of 

 trypanosome infection were from a single restaurant. The rats 

 were obtained from eighteen different places. 46, the largest num- 

 ber, coming from a single place, the restaurant just mentioned. 

 One animal from each of several places was secured. The num- 

 ber from each place thus varies too greatly and is too small in 

 manv cases to indicate valuable results. 



139 



