366 



BIOLOGY OF THE LABORATORY MOUSE 



caecum, ,1. Iclniplcni is more commonly found in the colon. Of the mice 

 examined by J. M. Twort and C. C. Twort, 43 of the colons of 57 animals 

 contained this parasite while only 3 of the caecae of 34 mice did. The two 

 parasites may be found together. 



These parasites can be distinguished in that the uterus or oviduct of 

 A. tetraptcra extends posterior to the anus, and also the tail of A. telraptera 



Fig. 147. — Syphacia obvelata. A, egg; B, female from the caecum of a mouse. 

 (Enlarged.) {From Augustine, after Ripley.) 



is short and bluntly pointed posterior to the reproductive organs, while that 

 of 5. obvelata is long, extending for some distance posterior to the anus. The 

 male of A. tetraptera measures from 2 to 2.5 mm. in length, and the female 

 from 2.58 to 4 mm. The eggs range from 84 /jl to go jjl in length by 34 fx to 

 40 jjL in breadth. 



This species is similar to S. obvelata in its pathogenesis and control. 



