88 THE TAPE-WORM. 



toidea pass, and be better able to bring them into unison with 

 the phenomena presented by the other entozoa, if, as has been 

 suggested above, we regard the scolices as agamozooids. 



In taking this view of the jaature of the scolices of the 

 Cestoidea, we assume that they are in that condition in which 

 they may, by asexual reproduction, bring forth a series of 

 sexual individuals. This in reality takes place, but only in the 

 intestinal canal of vertebrate animals. Before entering more 

 fully into the description of this process, however, it is advisable 

 that I should refer to certain facts, known to helminthologists, 

 which prove that the scolices really originate in the cestoid 

 embryos furnished with six booklets. In this matter I avail 

 myself of the evidence of Stein of Tharand, who made the fol- 

 lowing important observations. 



Stein discovered, 1 on the exterior of the stomach of the meal- 

 worm (the larva of the coleopterous Tenebrio inolitor), small cysts 

 about the size of a pin's head, containing a cestoid embryo in whose 

 body a more or less fully developed scolex was included. In 

 those that were fully developed Stein recognised a perfect Tania 

 head. Stein distinctly convinced himself that the Tania embryo did 

 not become a scolex by simple growth, but that the latter was 

 produced by budding in the body of the embryo, having, amongst 

 the numerous cysts that he examined, the most various transi- 

 tional forms, from the simple unaltered embryos to those con- 

 taining a fully developed scolex. During this development of 

 a scoliciform agamozooid the embryo changes its form, growing 

 rather longer on the one side than the other, in consequence of 

 which its six hooks become irregularly scattered over the upper 

 surface of the body and lose their import (fig. 26) ; a clear 

 proof that they do not enter into the formation of the circlet of 

 hooks of the tsenioid scolex. It is clear that these tsenioid 

 embryos arrive by immigration into the abdominal cavity of the 

 meal-worms, and in fact, as Stein suspected, through the walls 

 of the stomach ; for this observer more than once found tsenioid 

 embryos in the stomach of meal-worms, which, judging from their 

 form, could only just have been hatched. Most likely these 

 minute embryos had been taken in with their food by the meal- 



1 See his ' Beitrage zur Entwickelungsgeschichte der Eingeweidewnrmer,' in the 

 'Zeitschrift fur Wissenschaftliche Zoologie,' edited by Kolliker and myself. Bd. iv 

 1853, p. 207. 



