THE ASCIDIANS OF GUERNSEY. 



BY ERIC W. SHARP. 



The shores of Guernsey and the Channel Islands in general 

 have long been known to Marine Zoologists beeause of their 

 remarkable richness in species. Many eminent and well- 

 known scientists have worked here with great success in their 

 respective branches. Among others may be mentioned Canon 

 A. M. Norman, Dr. Gwyn Jeffries, Mr. J. T. Marshall, W. 

 Joshua Alder and Dr. Bowerbank. 



Although all forms of marine life are found here in 

 abundance and variety, none exceed the Ascidians in either 

 plentiful ness or striking coloration. These Ascidians form 

 what is perhaps the least known group of marine animals. 

 Very few people, outside the circle of naturalists, have 

 the vaguest ideas as to what they are and what they look 

 like. Hence it has been thought best to give an account 

 in this paper of their appearance, structure and life history. 



The name Ascidian is derived from tho Greek 44 Askos," 

 meaning a bottle, and this well describes the form of many 

 species, especially the simple forms. The other name for 

 these animals is " Tunicata," given them because of their 

 thick outer covering or tunic. 



The Ascidians are chiefly rock-haunting animals and 

 may be seen on practically any piece of our coast adhering to 

 rocks or seaweed. Some, however, are free-swimming and 

 lead pelagic lives far out in the ocean, while others live buried 

 in the sand. 



Many species live solitary lives attached to the rock by 

 their end or side. These are called the " Simple Ascidians," 

 and are generally of large size. Ciona intestinalis, a common 

 form with us, may reach the length of about eight inches. 

 In other species the individuals are grouped together into 

 colonies, not embedded in a common covering, but arising 

 from a creeping stem or stolon, which contains prolongations 

 of the blood system. These are known as the Social Asci- 

 dians. A third great group is made up of the Compound 

 Ascidians. These are colonies of small animals completely 

 embedded in a common covering. The colonies are often 

 [1910.] 



