Introduction to Animal Morphology. 201 



■oesophagus may be long (Hsementeria), or short, but 

 the stomach is long, with alternate dilatations and 

 contractions (Pontobdella), or with lateral caeca ; of these 

 Clepsine has six, Hirudo nine, Piscicola ten, Aulaco- 

 stomum only two. These may be branched as in Clep- 

 sine, reminding one of a dendroccelous Turbellarian. 

 The pylorus is surrounded by a sphincter, and the 

 straight intestine runs often between the two hindmost 

 caeca, which are longest, the only ones present in 

 Aulacostomum. The intestine may also have caeca 

 (Clepsine) and a pre-anal dilatation (Piscicola), The 

 ^nus is dorsal above the hinder sucker. 



The circulatory system contains often red blood, 

 the colour residing in the fluid, seldom in the corpuscles. 

 In most, the blood flows in the nearly obliterated 

 body cavity which here exists as a system of sinuses. 

 These may form two lateral pulsating vessels, and a 

 median sinus divided by the viscera into dorsal and 

 ventral vessels, which in Clepsine and Piscicola have 

 valves, but these around the pharynx are continuous 

 as a vascular ring, and freely anastomosing ; lacunary 

 branches from these vessels complicate their relations ; 

 some of these are contractile spaces in Nephelis. These 

 lacunae permeate freely the spongy dermis and mus- 

 cular layers. Respiration is dermal, and the lateral 

 vascular organs in Branchellion and Ozobranchus 

 may also be for breathing purposes. 



The excretory organs are tubes with glandular 

 walls, symmetrically arranged along the ventral 

 aspect, var}ang from two (Branchiobdella) to seventeen 

 (Hirudo), either closed internally, or opening within 

 by a ciliated, funnel-shaped orifice, while the outer 

 opening maybe on a lateral wart. A primitive set of 



