350 



THE DEVELOPMENT OF CESTODES. 



Thus we understand how it is that, in transverse sections of the 

 lower part of the rudimentary head (Fig. 192), we come upon some 



where the four suckers are seen all opening 

 into the central space. Such a section must 

 of course be above the hooks. I ought also 

 to mention that one frequently finds cases 

 where the apical surface is pushed out- 

 wards, 1 so that the hooks (Fig. 193) come 

 to be about the same level as the suckers. 

 I 'believe that this occurs especially in 

 specimens which have been suddenly 

 killed by spirit, &c., while in full posses- 

 sion of their powers of contraction. 2 

 Although this pushing outwards occa- 

 sionally occurs early, even before the 

 formation of the hooks (Fig. 188, O), I 

 think it is to be regarded as the result only of a secondary alteration, 

 probably determined by a contraction of the surrounding musculature. 



FIG. 192. Transverse section 

 of the anterior end of the bladder- 

 worm of the rabbit, at the level 

 of the suckers, (x 40.) 



FIG. 193. Longitudinal section through the head of a bladder- worm from the 

 rabbit, where the crown of the head is pushed outwards. ( x 60.) 



Before passing to describe the metamorphoses of the head, I may 

 remind the reader that the cavity is widened out at the lower end, 

 which, as the embryo grows in length, becomes ever more sharply 



1 The original here has " inwards " (nach Innen), referring to the cavity of the in- 

 vaginated head. I think it better to use the word " outwards," meaning " towards the 

 periphery of the bladder." W. E. H. 



8 I infer this from the fact that in my earlier investigations, which were mostly on 

 living specimens, this appearance but rarely occurred, while I observed it frequently when 

 working with hardened specimens. 



