Infrodnction to Aiiimal Morphology. 



165 



imperforate, rounded, or facetted, and has 2-4 round or 

 elongated, sometimes movable, suckers (Fig. 23, B), and 

 may be armed with hooks of chitin (calcified or silici- 

 fied ?), acting as anchors, placed often alternately in 

 circlets. The blunt ends of these are in pouches, and 

 their roots thicken with age. There are fine hairs on the 

 head and suckers in Triaenophorus, and on the hinder 

 €nd of the body in Tetrarhynchus. The head may 

 have a central spur (rostellum, cupula), or, as in 

 Tetrarhynchus, a Fig. 23. 



protrusible pro- 

 boscis, armed with 

 hooks. Behind the 

 suckers are occa- 

 sionally nerveless 

 red specks,perhaps 

 rudimental eyes. 

 The head is borne 

 on a neck which 

 begins narrow, but 

 rapidly widens into 

 the jointed body, which (except in Caryophyllaeidse) is 

 made up of 2-00 metameres. The body grows from 

 the head (the oldest part) to the distal end, so that the 

 neck metameres are the newest, and the oldest joints 

 are those most remote from the head. Each segment 

 as it ripens develops reproductive organs, and is 

 named proglottis, in which stage it may have a brief 

 separate existence. As the immature segments 

 (Strobila) show an inter-metameral continuity of 

 textures, and as there is a single water-vascular and 

 (when present) nervous system, the entire worm is 

 regarded as a persona, not as a colony. 



A, Proglottis of T. solium; a, water-vascular 

 system ; b, sexual orifice ; c, uterus ; d, testes ; e, 

 vesiculae seminales ; f, vas deferens ; B, head ot 

 T. medio-canellata. 



