ANIMAL PARASITES AND DISEASES. 67 



On the twenty-seventh day out of forty-three eggs opened only one 

 larvae was alive, and on the twenty-eighth day only one out of sixty- 

 five, and on the twenty-ninth day all the remaining eggs, one hundred 

 and three, showed only dead larvae. 



The results of this study it will be seen, confirm in the main the 

 conclusion of the former observations, the principal difference lying in 

 the fact that all the larvae were dead at a somewhat earlier period. 

 Of course it could not be said that of the eggs opened in the earlier 

 days none would have survived longer than four weeks, but consider- 

 ing the number used, and that one-third of them were kept the full 

 four weeks and two-thirds nearly that long before being opened, the 

 presumption is strong that that is the full normal period of survival. 



It is safe, I think, to sum up the matter by saying that the eggs 

 normally require friction and moisture to permit of their hatching and 

 transfer to the horse's mouth, that hatching occurs with difficulty 

 before the tenth day, and most readily after the fourteenth day, and 

 that they lose vitality at a period varying between the twenty-eighth 

 and fortieth days, the bulk not surviving more than four weeks. This 

 gives a solid foundation upon which to base recommendations as to 

 the time \vhen eggs must be destroyed." 



Before describing my own experiments, I should like very briefly 

 to deal with the views advanced by the above. 



Yerriirs statement that larvae are present in the egg when laid 

 I consider not entirely accurate. It is possible, indeed probable, if 

 after the fertilization of the eggs dull weather follows and the ova are 

 retained for some time within the parent, that this may be the case, 

 as I have recorded for Oestrus ovis, Linn., 1 and, further, I have an 

 egg taken from a torpid female, in which a fairly well-developed larva 

 is present, still in the ordinary course of nature I think we are not 

 warranted in stating that the eggs contain larvae when laid. 



The further statement that " moisture hatches the eggs " is 

 scarcely correct in the light of Osborn's experiments and those 

 recorded here. 



Froggatt's statements that the eggs are carried to the mouth and 

 hatch there is certainly wrong r and that of Bracy Clark's that the 

 " warmth and moisture is sufficient to bring forth in an instant the 

 latent larva," I am unable to verify. 



ijourn. Econ. Biology, 1906, vol. i, pp. 72, 73. 



