254 EMBRYOLOGY 



body-epithelium. They arise as "primitive muscle-fibres" in the 

 epithelial cells, and pass from these into the fibrous tissue of the sub- 

 cuticula. When this process is completed, the body-epithelium de- 

 generates completely and disappears. The formation of the lemnisci 

 agrees with that of the skin. The nuclei, which have separated from 

 the central mass and moved to the anterior end of the body, here form 

 a circular swelling which at two diametrically opposite points is drawn 

 out into slender processes, the fundaments of the lemnisci. In them 

 the formation of the fibrous tissue takes place just as in the skin. Near 

 the anterior end of the body, and immediately behind the rod-like pro- 

 boscis, there also lies an extensive mass of nuclei, the fundament of the 

 central nervous system, from which the peripheral nerves soon grow out 

 to the different organs. 



The organs the development of which has thus far been described 

 are said to be of ectodermal origin ; this, indeed, is very probable, 

 although sufficient grounds for this conclusion cannot as yet be recog- 

 nized in Kaiser's description. The real body-musculature, the sexual 

 glands, and the ducts of the genital apparatus arise, according to Kaiser, 

 from the entoderm. Leuckart had spoken of a mesoderm, which splits 

 into an outer and an inner layer, but as yet Kaiser has not given 

 attention to this statement. Again, it is layers of nuclei which separate 

 from the central mass to give rise to new structures. Three such layers 

 of nuclei can be recognized, owing to their somewhat different shape. 

 The two outer ones soon migrate to the body- wall, and here, after various 

 metamorphoses, supply the circular musculature and the longitudinal 

 musculature of the body. 



Behind the proboscis, in the neighborhood of the ganglion, are found 

 nuclei, arranged in definite order, concerning whose origin more accurate 

 knowledge would be important, for out of them arise the proboscis-sheath 

 and the retractors as well as other muscles of the proboscis, therefore 

 structures which would be ascribed to the inner layer of the mesoderm 

 did such exist. 



The formation of the genital oi'gans takes place in quite a peculiar 

 manner. Behind the proboscis-sheath a prismatic protoplasmic mass 

 makes its appearance, from the edges of which arise four thin plates, 

 which divide the cavity of the body into four sectors. By this descrip- 

 tion one is mvoluntarily reminded of the mesenteries which unite the 

 fundaments of the genitalia with the body- wall, and at the same time 

 recalls the conditions which, according to Vejdovsky, exist in the 

 Gordiidse. In the female the plates unite in the dorsal and ventral 

 sectors to form the ligament ; in the male the plates of one sector 

 degenerate. The germ glands themselves arise from the axial mass of 

 plasma. The resemblance of the thin plates to mesenteries, referred to 

 above, is increased, as far as can be judged from the brief statements of 

 Kaiser, by the two lateral sectors being filled with a cellular mass; 

 subsequently, however, this degenerates and thus gives rise to the body 



