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salivary glands in the thorax ; but the tsetse fly has them in the 

 abdomen, similar to the rat-flea. The explanation is that the 

 arrangement is an adaptation to the extremely muscular thorax, 

 and every other organ is reduced in dimensions ; and so, among 

 other things noticeable, we find the salivary glands carried right 

 back to the abdomen, Avith as small a duct as possible. It was 

 curious that the only two kinds of insects he ever dissected should 

 both have the salivarv glands carried back to the abdomen. He 

 had occasionally found in the fleasa cysticercoid, which was proved 

 by actual experiment to be a larval stage of the tapeworm of the 

 rat, Ili/menolepis diminuta. The flea became infected during its 

 larval stajje. The flea larvae often feed on the faeces of the 

 rat, and ingest the eggs at this stage. There is no doubt what- 

 ever that the life -cycle is completed by the rat catching and eating 

 the fleas. The host of this intermediate stage was previously 

 unknown. About 4 per cent, of the fleas examined were infected, 

 and sometimes two or three cysticercoids were found in one 

 specimen. Recently a second cysticercoid had been found. The 

 first form had no hooks, but the second had a notable circle 

 of hooks. Only two specimens had, so far, been found, and 

 these were not yet positively identified, but were believed to be 

 Hymenolejns murina . 



The preparations exhibited were : ( 1 ) Cysticercoid of the rat- 

 tapeworm, Hymenolejns diminuta, from the body-cavity of the 

 rat-flea, C eratophyUus fasciatus, with head invaginated ; (2) the 

 same, with head extended ; (3) another species of cysticercoid, 

 probably //. murina, also from the body-cavity of the rat -flea ; 

 (4) ventral nervous system of the flea, C. fasciatus ; (5) salivary 

 glands, and duct of the same. 



Mr. D. J. Scourfield, F.Z.S., F.R.M.S., then read a paper on 

 ^' The Use of the Centrifuge in Pond-life Work." 



Mr. C. F. Rousselet said they were much indebted to Mr. 

 Scourfield for explaining several difficulties not infrequently met 

 with. If rotifers were kept for a few days, it was found that 

 their stomachs became empty, and at the end of a week they were 

 all dead. It would be very useful to know what kind of small 

 organisms such creatures used as food, as we should then be able 

 to supply it, and keep specimens alive for a longer time. 



Mr. Gabb said the application of the principle of the centrifuge 

 was due to Laval, who in 1885 invented what he called the 



