134 



INVERTEBRATE ZOOLOGY 



entoderm to form even a rudiment of an alimentary canal. As 

 adults they occur normally in the digestive tract of vertebrates. 

 The first larval host is practically always an arthropod, though 

 young individuals have been found frequently in other hosts 



Proboscis 



Recspfade — U- 



HHrachns of- 

 recep^cle 



\Liaam07f 



Cemenf 

 glands 



. Bursa 



A B 



Fig. 71. — Morphology of the Acanthocephala. A, general organization of 

 male of Acanthocephalus ranac (Schr.) ; B, interior of caudal extremity of a young 

 female of Neoechinorhynchus emydis, showing genital tract. {After Van Cleave). 



which probably act as intermediate hosts. In the digestive 

 tract of the vertebrate, the acanthocephalan has an elongated 

 flattened body form but upon removal to water or killing fluids 

 the liquids distend the body to cylindrical form. One of the 

 most characteristic structures is the proboscis (Fig. 71 A) at the 



