CAUDAL APPENDAGES. 



Fig. 26. 



The changes of those cestoid embryos in which the receptacle 

 grows out behind into a long, solid, caudal appendage, are very 

 remarkable. The receptacle of the Tcenia scolex which Stein 

 observed in the meal-worms, de^velopes such an appendage (page 

 38). I must remark here, that Stein considers the scolex recep- 

 tacle as a cyst, and the caudal appendage as a part of it, which 

 is certainly not correct, for if the tail does not appertain to the 

 embryo, how could the six hooks have come to lie upon the 

 upper surface of the tail, where, according to Stein's express 

 assertion, he invariably saw them ? 



The Piestocystis crispa, which attains a length 

 of from one to three inches, is nothing more than 

 a Tcetiia scolex evolved from its receptacle, with a 

 very long, ribbon-like, solid, caudal appendage. 1 In 

 certain Tetrarhynclti the receptacle also becomes dis- 

 tended into a vesicle, and such forms of Tetrarhynchi 

 were united by the older helminthologists into the 

 genus Anthocephalus. From this genus Diesing 

 separated, under the names of Acanthorhynchus and 

 PteroboHdum, those Tetrarhynchus scolices, the pos- 

 terior end of whose receptacle is produced into a 

 very long, unjointed, caudal appendage. As in 

 .these degenerations, the form and size of the vesi- 

 cular dilatations of the receptacle, as well as the 

 shape and length of its caudal appendage, are often 

 dependent upon accidental external influences, the 

 dissimilarity which the parts present in different individuals of 

 one and the same species of scolex become readily intelligible. 

 For this reason, such diagnostic characters of genera and species 

 as are derived from the conformation of the vesicular enlarge- 

 ments and of the caudal appendages of the receptacle must be dis- 

 carded on account of their uncertainty. Only on the form of 

 the scolex (the so-called head of the sexually matured cestoids) is 

 it possible to base constant generic and specific characters. A 



Fig. 26. A Tania scolex from the meal-worm retracted within its receptacle; 

 partly after Stein, a. Head of the scolex. b. Receptaculum scolicis. c. Caudal 

 appendage of this receptacle, on which lie scattered the six embryonic hooks. 



1 This animal was formerly described by Rudolphi as Cysticercus crispus. I have 

 demonstrated, however, in the ' Zeitschrift fur Wissenchaftliche Zoologie,' (Bd. ii, 1850, 

 p 223), that this worm possesses no caudal vesicle. 



