FOEM OF THE EUDIMENTAEY HEAD. 



463 



The rudimentaiy head of the smallest bladder-worms appeared, on 

 close inspection, as a short cylinder 0'35 mm. across, and 0'6 mm. 

 long. The receptacle was always in close contact with the outer 

 surface. The sharp bend which is prominent in the Cysticercus cellu- 

 losce at a still earlier stage (p. 348) is not to be seen here, although 

 the cavity of the head is already considerably expanded at the lower 

 end, and the narrow neck is not unfrequently contracted into a coil. 

 I was struck by the presence of numerous small granules (0'007 mm.) 

 which filled the greater part of the cavity of the head (Fig. 265), and 

 by their firmness, resistance to chemical reagents, aid optical charac- 

 ters, reminded me forcibly of the chitinous balls observed in the male 

 genital pouches of the young stages of Pentastomum.'^ The entrance 

 into the head-cavity formed a transverse slit, which crossed the 

 longest diameter of the body of the bladder-worm at right angles. 

 Eound about this slit several small calcareous bodies were to be seen. 

 The wall of the bladder was penetrated by a rich vascular network, 

 some branches of which passed into the insertion of the head, and were 

 continued into the substance of the latter. 



Fio. 265. — Head-rudiment of 

 Cysticercus Tcenia saginatm before 

 the development of the suckers, 

 (x 25.) 



Fig. 266. — Head -rudiment of 

 Cysticercus Tcenice saginatm after 

 development of the auckera. ( x 

 25.) 



The larger bladder-worms of the extracted muscle were manifestly 

 older phases of the above. Their head-rudiment had grown with the 

 body to a size of O'8-l mm. The lower portion of the head-cavity had 

 enlarged to a spherical space of almost 0'5 mm. in diameter. The 

 pockets for the suckers were formed, and were almost all clad with 

 their muscular sheaths, though the disposition of the head was essen- 

 tially the same as before (Fig. 266). 



What struck me most in regard to these bladder-worms was the 

 fact that they, although the descendants and young forms of a hook- 

 less tape-worm, were furnished with a distinct though small rostellum, 

 and with the rudiments of hooks. This was all the more striking, 



* Leuokart, "Bau und Entwiokelungsgesoh. d. Pentastomen," p. 140 : Leipzig, 1860. 



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