as affecting Domesticated Animals. 59 



from which in G days' time, other young lice arc produced : upon this su])po- 

 sition the number of lice springing from 2 females will amount to 10,000. 

 Thus it appears that the 2 females may in 8 weeks' time he grandmothers, and 

 see 10,000 lice of their own offspring, which unless reduced to actual demon- 

 stration would seem incredible ; and who can tell whether in the heat of sum- 

 mer these creatures may not breed in half the time I have mentioned? " 



Whetter these hypotliescs with regard to the reproductive 

 powers of the louse be absolutely correct or not, we see quite suffi- 

 cient in the experiment itself to explain the fact of one lousj 

 animal quickly contaminating another, and often an entire herd. 

 Leeuwenhoek's experiments being made with lice of the human 

 subject, the parasites found in him a proper host, and consequently 

 his conclusions with reference to the deposit of eggs, and the time 

 necessary for the production of the^?'s^ hatch, would be correct. 

 Whether similar experiments, of transposing lice of the horse or 

 ox, to other horses or oxen, as proper hosts, would give a result con- 

 firmatory of Leeuwenhoek's suppositions of the rate of increase, 

 remains to be proved. As yet we have had no opportunity of 

 testing this by direct experiment. We have, however, very fre- 

 quently collected the ova of the different kinds of lice, and 

 adopted means of keeping them under daily observation, and at 

 a temperature equal to that of the animal body, so as to deter- 

 mine the period of incubation. The results seem to show that 

 the time Avhich elapses between the deposit of the ova of the 

 IIcBmatopiiiiis Bovis, for example, by the parent louse, and the 

 birth of the young ones, is about twelve or fourteen days. We 

 have frequently known a hatching to take place as late as the 

 fourteenth day, but never after that time. On obtaining ova 

 from the bodies of animals for a purpose of this kind, it is found 

 that some of the young will be hatched even on the first or second 

 day afterwards, and others at different intervals up to the date 

 named. This variation in the time is due to the circumstance 

 that the ova when taken are not all of the same age, and conse- 

 ((uently the young lice are in different stages of development. 

 It is almost impossiljle to distinguish the fresh-laid eggs from 

 the older ones, so that correct conclusions as to the period of 

 incubation can only be arrived at from the Jatest births, the ova 

 yielding these young lice having been laid by the parent pro- 

 bably on the very day they were procured. 



The matured ova are expelled singly from the uterus of the 

 parent, and each one in succession is attached by a glutinous 

 material, which is voided with it, to the lower part of a hair, 

 near to its root. Sometimes three or four ova will be found 

 adhering to the same hair ; but generally only one is met with. 

 Each c^^ is so fixed as to leave the larger end free, which is always 

 directed towards the point of the hair. The a^'g is also attached 



