THE TUNIC ATE S AND THE LANCELET. 





this it is not necessary to go into the anatomy and developmenl 

 these forms. 



The tunicates are both simple and compound; that is, some of them 

 live a solitary life, while others are united into large masses with a com- 

 mon integument, and some of these organs also serving for all the colony, 

 a condition recalling that occurring in some of the hydroids 3 described in 

 an early part of this volume. 



The general appearance of one of the simple forms is shown in our cut. 

 There are two openings to the body: into one of them the water streams, 

 carrying with it food and oxygen, while from the other flows the w 

 which has fulfilled its purposes and with it the waste products of the 

 body. A common name for these animals is sea-squirts, from the fact 

 that when touched they contract as far as possible, forcing the water out 

 of the openings. Some of the species are also known 

 as 'sea-peaches' and ' sea-pears,' in allusion to their 

 shapes and colors. 



The compound forms are, as a rule, smaller than 

 the simple ones. The form figured is very common 

 on sea-weed and rock-weed all along the shores of the 

 ocean, different species occurring in different seas. As 

 will be seen, the animal has a somewhat star-like 

 appearance ; the rays of the stars are each the incur- 

 rent opening to the body, comparable to that of the 

 simple form, while the spot in the centre is the excur- 

 rent orifice, used in common by all the members of 

 the colony. 



One of these compound forms, Pyrosoma (fire- 

 body), needs special mention. It is an inhabitant 

 of the tropical seas, and reaches a length of two or 

 three feet. In these the individuals are arranged so 

 as to form a large cylindrical tube, the cavity of 

 which forms the excurrent orifice of the colony. 

 Most remarkable about these forms is their phos- FlG . 288 



rp, cate i /•'■ •■"■■ • 1; : 



phorescence, which is described as very great. Iney piece oi 

 move slowly through the water, appearing on dark 

 nights like a mass of fire, and the story runs that one natural u 

 description of the beautiful appearance they present, and thei 

 account by the light which the animal itself afforded. 



Strangest of all are the Salpas, delicate, transparent forms wli 

 the warmer seas. Sometimes they occur singly, sometimes in 

 of individuals adhering together, and it has been found out that 



