ON' TWO SPKCIKS OF CVSTICEilOOIDS. 9 



" By whatever name it is called, this hybiid is undoubtedly a 

 homozygote for pattern and coloni-, pine and permanent, trans- 

 mitting these characters to its descendants. Cross-breeding 

 between these two varieties of Thamnalea pi'oduces a new form, 

 owing possibly to the meeting of characters never previously com- 

 bined, and as they are constant it is evident these have an affinity 

 and have become insepai-able. 



" On such lines Evolution might be conceived as having pro- 

 ceeded fairly rapidly towards the sepai'ation of species. 



" Some while ago 1 showed a hybrid hen whose pure Swiiihoe 

 plumage had been transmitted through the cock. To-day the 

 skin of her son, a pure iSwinhoe cock, is exhibited for your 

 inspection. 



'' An account of my method and management of these Pheasant- 

 breeding experiments has been already published in the ' Pro- 

 ceedings ' (1909, p. 885), showing the care and precautions used." 



Two iSpedes of C ysticercoids from the Rat-flea (Ceratophyllu.s 

 fasciatus). 



(Text-figures 1 & 2.) 



Dr. W. NicoLL and Professor E. A. Minchix, M.A., Y.P.Z.S., 



exhibited examples of two species of Cysticercoids which had 

 been found in the body-cavity of the i-at-flea {Cerato2yhylh(,s 

 fasciatus) dissected by Professor Minchin in the course of in- 

 vestigations upon the development of Trypanoso'ma leioisi in the 

 flea. 



The first specimen shown (text-fig. 1) was one previously ex- 

 hibited by Piof. Minchin (P. Z. S, 1909, p. 741). >Since "then 

 experiments had been carried on by Dr. Nicoll at the Lister 

 Institute, which proved that it was the larval form of Hymenolepis 

 dimiiiuia, and threw light upon the mode of infection. This 

 Cysticercoid had occurred in about four per cent. (8 in 207) of all 

 the fleas examined during a period of thirteen months. It was 

 found in the body-cavity and usually only one specimen at a 

 time. As many as three, however, had been found in one flea. 



In the reti'acted state the Cysticercoid consisted of a flattened 

 oval body and a moi-e or less elongated tail. The dimensions of the 

 body were '31 x '25 mm., and the tail might be as much as "8 mm. 

 long. The wall of the body consisted of a number of well- 

 difierentiated layeis. The outermost layer was non-cellular and 

 bore a cei'tain resemblance to cuticle. It was marked by fine 

 radial striations. The second layer consisted of columnar cells, 

 each with a large and distinct nucleus. ISTeither of these layers 

 occurred in the tail. The third layer w-as parenchymatous, 

 consisting of a large number of irregularh' disposed cells. This 

 was continuous with the substance of the tail. The next layer 

 was apparently of a fibrous nature, consisting of a few cells set 

 in a mass of circularly arianged fibres. This layer was sejmrated 

 from the next by an intervening space. This was seen usually 



