244 EMBRYOLOGY 



bodies of two hosts. Its development differs from that of 

 other Nematodes in that the young born of the sexually 

 mature females in the intestine of the host do not reach the 

 outside world, but break through the walls of the intestine 

 and migrate into the muscles of various parts of the body of 

 the host, to become, after sufficient growth, encysted. In 

 order to wake the muscle Trichina into new life and bring 

 about its sexual maturity, it is necessary that the infected 

 muscle be consumed by some other animal, in whose intes- 

 tine the Trichinae then attain their complete development 

 and power of reproduction (Leuckart). 



II. GORDIID>E. 



The accounts of the development of the Gordiidse are still 

 superficial. The eggs are not deposited singly, but are united 

 into large balls or strings ; for during oyiposition a tenacious 

 mass is poured over the eggs, which are already surrounded 

 by a shell. The mass hardens in the water. Since the egg- 

 strings are heavier than water, they sink to the bottom and 

 remain thereuntil their embryonic development is completed. 

 This does not begin until after the laying of the eggs, and 

 requires quite a long time, according to Meissner about a 

 month or more. As regards the first stages of development, 

 the statements of the authors (Villot, No. 16, and Camerano, 

 No. 11) do not agree. According to Camerano, the cleavage 

 is nuequal, and leads to the formation of a bilaminar cell- 

 plate, which, by the bending in of the edges, is metamor- 

 phosed into a gastrula with a long slit-like blastopore, in a 

 manner similar to that described above (p. 235) for Cucul- 

 lanus. The gastrula closes, exactly as in Cucullanus, from 

 behind forwards. The observations of Camerano on Gordius 

 Villoti extend up to this stage, and it appears as if the 

 figures given by Villot for Gordius aquaticus could be ap- 

 plied to Camerano's observations. Villot describes the 

 cleavage as regular. A solid heap of cells arises which, 

 after further multiplication of the cells, splits into a central 

 cell-mass and a peripheral layer (Villot). The hitherto 

 spherical embryo elongates somewhat, and a deep depression 



