THE CYSTIC ENTOZOA. 49 



To prove that the cystic Entozoa are the sexless and va- 

 riously degenerated nurses of the Cestoidea, I must once again 

 return to the already mentioned (page 36) development of the 

 cestoid agamozooids. When the cestoid embryo has immigrated 

 and established itself in any organ of an animal, it begins to 

 develop a scolex by internal budding, which takes the form of a 

 Tcenia-hesid or of a Tetrarhynchus-he&di, &c., according to the 

 origin of the embryo. The embryo then increases and becomes 

 enlarged by the growth of the scolex, which it holds enclosed 

 within the distended walls of its body. These walls pass inter- 

 nally into the neck of the scolex, directly over the spot whence 

 the scolex sprung. On the external surface a funnel-shaped but 

 narrow depression is developed opposite the scolex, from which 

 a canal stretches through the neck of the scolex to its head. 

 This canal, after the full development of the scolex, permits its 

 evolution, by which means the hinder end of the scolex passes 

 immediately into the body of the embryo. The fully developed 

 scolex in the interior of the embryo appears as if it had drawn 

 itself inwards by a process of involution ; but observation teaches 

 us that the scolex is originally developed in this involuted con- 

 dition, instead of becoming retracted when it has attained its full 

 development. The material required for the development of 

 the scolex and of the embryo which invests it, is taken up by 

 the latter by absorption through its integument. This absorptive 

 power of the integument may vary in amount, and produce 

 different results, which are, of course, dependent upon the 

 quantity and quality of the fluids, and upon the special pecu- 

 liarities of the organs of the animal in which the embryo has 

 taken up its residence. Under particular circumstances it may 

 easily happen that an embryo should absorb, through the surface 

 of its integuments, more nutritive fluid than is necessary for the 

 growth and development of the scolex. The surplus nourish- 

 ment then gives rise to exuberance of growth and to degenera- 

 tion of the body of the embryo. The immediate consequence of 

 the accumulation of absorbed and unemployed nourishing juices 

 will be a vesicular enlargement of the embryonic body ; and the 

 cestoid embryo in this condition has received the name of a 

 cystic worm. The development of the scolices in such cystic 

 entozoa is sometimes more, sometimes less, advanced. 



I have already shown that the cestoid embryos, after leaving 

 their eggs, must wander, in order to establish themselves in 



4 



