354 



NOTES on VARIATION in the TUNIC AT A. 

 By W. A. Herdman, D.Sc, F.L.S., 



PROFESSOR OP NATURAL HISTORY IN UNIVERSITY COLLEGE, LIVERPOOL. 



It is often a matter of very great difficulty to fix upon good 

 diagnostic characters in the Tunicata, and to distinguish 

 between allied species, and varieties, and mere individual 

 variations. I propose to discuss in this paper the most 

 reliable characters for making use of in describing the 

 species, and to give examples of some of the variations to 

 which these and other parts of the body of an Ascidian are 

 liable. 



In the first place, it is quite absurd to attempt to 

 describe, or even, in most cases, to identify, an Ascidian, 

 without dissection and microscopic examination. As Savigny 

 long ago said,* ''Les Ascidies ont I'organisation variee et 

 I'aspect uniforme. La configuration qui leur est afi'ectee ne 

 permet pas que les differences interieures se manifestent 

 au-dehors par des signes fort sensibles. Aussi les distinc- 

 tions necessaires a la parfaite connaissance des especes sont- 

 elle difficiles a tracer." 



In some cases the genus, and even sometimes the 

 family, cannot be determined without dissection. For 

 example, in many museums and other collections, all 

 Simple Ascidians which are incrusted with sand and shell 

 fragments are labelled " Molgulaj" but some of these speci- 

 mens usually belong to the genus Eugyra (to distinguish 

 which the branchial sac ought to be examined), and in 



* MemoireSf p. 84. 1816. 



