68 ENTOZOA OF RATS AND MICE. 



rinus and placed in water on 2nd Aug. 1909, the majority 

 segmenting by 26th Sept., embryos being found in several 

 on 30th Oct. 1909. No further changes were noted between 

 that date and 13th July, 1910, the embryos being ahve but 

 still Anthin the shell. 



Eggs taken from E. rattus. E. norvegicus and Mus 

 musculus were immersed in water on 28th April, 1910, a 

 few showing two-celled segmentation on 10th May. On 

 loth June there were 2, 4 and 8 cell stages but most of them 

 showed a multicellular condition while in one egg the outline 

 of a vermiform embryo was A'isible. A month later the 

 same stages were to be seen though immatvire embryo worms 

 were more abundant. A month later (10th October, 1910) 

 practically all the eggs contained mature embryos and these 

 continued to live for manj' months until killed by accidental 

 dessication. 



In another case, eggs from E. norvegicus immersed on 

 30th Dec. 1909, were found to contain fully-formed embryos 

 on 29th Jan. 1910, i.e. in about thirty da3's in midsummer. 

 Some of the eggs were alloA\ed to dr}- overnight and then 

 replaced in water in a room. About 30% failed to develop, 

 though development of the rest was retarded somewhat, 

 embryos appearing to be fully formed nearly three weeks 

 later than in the case of eggs not allowed to dry. 



Eggs placed in a tube with water and exposed to the 

 sun and weather continuously, Avere all killed -srithin 30 days. 



Bancroft gives egg )neasurements as o5 micra by 30 

 to 35 micra : Hall 40 to 52 in length by 30 to 35 in breadth ; 

 Davaine 50 to 55 in length ; Railiiet 52 to 55 hy 29 to 32 ; 

 Galli-Valerio 50 by 22. My measurements show a range 

 in length from 46 to 60 inicra, and \n breadth from 28 to 32. 

 The shell is about 3.5 micra thick, and the polar openings 

 have a diameter of 7 micra. The stip])led appearance of 

 the shell has already Ijeen noted. 



Bancroft gives 156 micra as the length and 7 as the 

 breadth of enbryos extruded from the shell. I found the 

 length to vary from 160 to 195 micra and the breadth from 

 5.5 to 7 micra. The anterior end is shghtly narrower than 

 the other. The cuticle is quite smooth and the body con- 

 ains abundant round fat-like sriobiiles. 



