128 



wards in the dorsal but the continous flow, in the compressed animal 

 at least, is feeble and indefinite. The corpuscles after being driven out 

 of one tree are carried along the lateral vessels in the stream caused by 

 the contraction of the tree, then they are either sucked back again by the 



Fig. 3. Cephalic loop and anterior ends of lateral vessels with small vascular 

 trees, from a young specimen. 



same tree or if carried far enough, sucked in by another. The pulsations 

 of the trees are probably controlled by the dorso-ventral muscle fibres 

 which are present in the pharyngeal region. Posteriorly the trees differ 

 very considerably from those in the pharyngeal region. Their 



Fig. 4. Right half of sucker showing anastomosis of vessels, and vascular 

 prolongations. 



origins are irregular, they lose to a large extent their tree-like form 

 and may anastomose with one another either with those of the oppo- 

 site side or with similar prolongations from the dorsal vessel forming 

 a very irregular system of vessel-commissures which varies consider- 

 ably in different specimens. 



