184 THE ANATOMY OF INVERTEBRATED ANIMALS. 



refracting corpuscles are scattered through the substance of 

 the body (Fig. 48, A). It is probable that these are more or 

 less calcined connective-tissue corpuscles. Similar bodies 

 which occur in some Trematoda were found by Claparede to 

 be lodged in dilated ends of the water-vessels, but it would 

 appear that they are not so situated in the Cestoidea. 1 



The distance between these transverse grooves, and their 

 depth, increase toward the hinder end of the body ; and each 

 segment is eventually found to contain a set of male and 

 female organs. The genital organs are constructed upon the 

 same general plan as those of the Trematoda, but the uterus, 

 as it fills with ova, usually takes the form of a ramified sac. 

 At the extreme end of the body, the segments become de- 

 tached, and may for some time retain an independent vitality. 

 In this condition each segment is termed a proglottis ; and 

 its uterus is full of ova. 



The embryo is developed in these ova in the same way as 

 in the Trematoda / and, as in the latter group, it may either 

 be ciliated (as in J3othriocephalus) or non-ciliated, which last 

 is the more usual case. The embryo is a solid morula, on one 

 face of which four or six chitinous hooks, disposed symmet- 

 rically on either side of a median line, are developed. 



Fig. 47.— Diagrams illustrative of the relation between Tcenia, Cysticercus, Coenurus, 

 and Echinococcus.—A, B, young: Tcenice, in the Scolex stage, the latter with an 

 enlarged receptaculiim Scolicis, into which the head and neck are withdrawn in 

 C, Cystieercus ; />, Cainurus ; E, hypothetical condition of Echinococcus, in which 

 " Tcenia heads " are developed only on the inner surface of the primary cysts; F % 

 JSchinococcus with secondary cysts; G, embryo Tcenia (after Stein). 



If the egg is placed in appropriate conditions, the hooked 

 embryo emerges from the shell, and rapidly increases in size. 



1 Sommer and Landois, " Ueber den Bau der geschlechtsreifen Glieder 

 von Bothrhocephalvs lotus?' 1 (Zeitschrift fur wiss. Zooloqie. 1872). Leuckart, 

 however, maintains the contrary opinion, " Die menschlicnen Parasiten," p. 

 175. 



