Summary. yj 



the branchial chamber. In the action of this heart a 

 curious appearance is observed ; the blood is driven 

 by this vessel first from one end to the other, for a 

 second the action stops, then it is resumed in the 

 opposite direction, again another cessation, and 

 another reversal, &c. 



The * tunic/ or outer wall (/) contains a starch-like 

 compound which is interesting as it is almost the only 

 instance of the occurrence of a starch-like compound 

 in the Animal Kingdom. 



Young tunicates as they emerge from the egg 

 appear as small, tailed larvae, with bodies consisting 

 of two cavities. The axis of the tail consists of a 

 cartilaginous or gristly rod : in one cavity of the body 

 the nerve ganglion is developed, in the other space the 

 viscera are formed. Thus they foreshadow the struc- 

 ture of vertebrate animals. 



Tunicaries are sometimes solitary, but many species 

 are found united into social assemblages, and this 

 union may go as far as the perfect union of the 

 blood-vessel systems, a single vascular apparatus sup- 

 plying the whole colony. In one group, the Salpae, 

 there is an alternation of generations, solitary and 

 colonial forms succeeding each other in a cycle. 



Many of the tunicates are phosphorescent, 

 Pyrosoma, a compound form inhabiting the Atlantic 

 ocean, being the most vividly luminous animal met 

 with in the seas. 



Summary. The chief types of worms may be 

 tabulated thus : 



i. Unjointed, ciliated, non-parasitic forms without 

 ciliated head-lobes = Class Turbellaria, 



