354 



THE DEVELOPMENT OE CESTODES. 



Fig. 200. 



Fig. 201. 



Pigs. 200 and 201. — Rndimentary 

 heads of Tcenia serrata at the beginning 

 (Fig. 200) and at the end (Fig. 201) of 

 the protrusion of the head. ( x 20.) 



pushes itself forwards even into the cylindrical body. In this way 

 the cuticular coat comes to lie externally, and the suckers are found 



under the hooks. When this eleva- 

 tion is complete, as in Kg. 201,^ 

 then the head is in position and 

 character like the subsequent tape- 

 worm head, and that the more since 

 the inner surfaces', formerly external, 

 soon come into close contact, and 

 form an apparently solid mass. 



Such appearances have often 

 given rise to the supposition that 

 the bladder-worm had this position 

 and form from the ver}' first. Ac- 

 cording to this theory, what we 

 have above described as the rudi- 

 mentary head, and have followed in its metamorphosis step by step, is 

 only a sheath, from the base of which the head subsequently arises as 

 a solid projection. 



Moniez, the last author who has discussed the Cysticerci, beheves 

 he has convinced himself of the truth of this by sections, and ex- 

 plains my opposing, and as he thinks erroneous, results by referring 

 them to my imperfect methods of investigation. It is, of course, true 

 that I first reached these results from the examination of squeezed 

 preparations (1856), but I did not neglect to corroborate them by means 

 of sections when our methods became more perfect. These later obser- 

 vations lead me still to persist in upholding the accuracy of the above 

 outlines, in spite of Moniez's opposition. Moniez has obviously confined 

 his observations mainly to old bladder- worms {Gysticercus pisiformis), 

 whose heads have often, as we have noted, lost their original position, 

 and are therefore unfitted to lead one to a true understanding of the 

 mode of origin. The young forms of which he made sections were, as 

 I could see from his preparations, at a stage when the head and its 

 cavity had still but a somewhat undifferentiated formation. 



What Moniez considers as the beginning of the head is only a 

 boss-like swelling of the base, such as (see Fig. 196) one not unfre- 

 quently finds in violently killed bladder-worms. Far from represent- 

 ing the whole head, this projection is, as we have seen, neither more 

 nor less than its apex with the lenticular rostellum, which, when there 

 is no protrusion, is seen in the form of a meniscus (Fig. 194), with 

 incurved anterior surface. If Moniez had investigated the proper 

 stages, he would have been convinced that the suckers, instead of being 



The figure is copied frqm a preparatipn kindl; 



^ ^ DigWze&liy Microsoh 



lent to me by M. Moniez. 



