588 THE INVERTEBRATA 



matous connective tissue between them. A dorsal vessel above the 

 alimentary canal widens over the notochord in the hinder part of the 

 proboscis into a space known as the heart. This is covered by a 

 vesicle known as tho, pericardium, whose lower wall, contracting, com- 

 municates pulsations to the blood. From the heart the blood passes 



^ A 



Fig. 440. 



Fig. 441- 



Fig. 440. A longitudinal horizontal section through Glossobalatius. Diagram- 

 matic. From Shipley and MacBride. al. alimentary canal ; br.s. branchial sac 

 with external opening; col. collar; col. ca. collar cavity; d.b. dorsal blood 

 vessel; g. reproductive organs; gloni. glomerulus; h. heart; pern, peri- 

 cardium; peh. perihaemal cavity; por'. collar pore; por. proboscis pore; pro. 

 proboscis; pro.ca. proboscis cavity; trk. trunk. 



Fig. 441. A Tornaria larva. From Sedgwick, after Metschnikoff. a, From 

 the left-hand side, h, From the dorsal side. A, anus; C, pericardium; 

 M, mouth ; P, rudiment of right middle (collar) coelom ; P' , rudiment of 

 right hinder (trunk) coelom ; S, apical sense plate ; W, rudiment of anterior 

 (proboscis) coelom. 



into a plexus contained in an organ known as the glomerulus, which is 

 formed by a puckering of the hinder wall of the proboscis cavity 

 around the end of the notochord. It is thought that this organ acts 

 as a kidney, taking waste matters from the blood and throwing them 

 into the proboscis cavity, whence they are expelled through the pro- 



