330 W. G. Van Name — Bermuda Ascidians. 



such a nature that it is reasonably certain that they are not merely 

 individual peculiarities of the specimen. 



Minute and careful description cannot make up for insufficiency of 

 material. Indeed it often decreases rather than increases the possi- 

 bility of positively recognizing the species again if the individual 

 peculiarities of the specimen be described as specific characters, and 

 if no indication is given in regard to the directions in which indi- 

 vidual variation (which is vastly greater in the ascidians than most 

 writers give credit for) may be expected to manifest itself. 



In the case of some Bermuda forms, the amount of material avail- 

 able has not been as great as could be desired, yet in nearly all cases 

 I have had several specimens collected at different times and places. 

 In two cases only have I ventured to describe a species on the 

 strength of a single colony (Didemnum solidum and Diplosoma 

 atropunctatum), and these only where there were well-marked 

 specific characters, and when I had examined the specimen in a liv- 

 ing state. In fact, there are only two or three of the forms which I 

 have not myself collected and studied in a fresh condition. 



The almost total neglect of the Compound Ascidians of this part 

 of the world by previous collectors and investigators sufficiently 

 explains, I think, the large number of new species in that group. 



Methods of Collecting. 



Most of the species may be found attached to stones along the 

 shores of the bays and harbors, at low water. They grow chiefly 

 on the under sides of stones of sufficient size to resist the movement 

 of the waves and currents to which they are exposed. In such 

 situations, as well as in narrow crevices in the rocks, they are safe 

 from the attacks of the fishes and larger animals of other kinds 

 which would otherwise destroy them. 



The limestone rock, of which the islands are composed, contains 

 numerous caverns to which the sea water has access through narrow 

 passages where there is always a current of water when the tide is 

 rising and falling. About the mouths of these passages (as at 

 Waterloo, on Castle Harbor) are the best collecting places, not only 

 for ascidians but for many other forms of invertebrates as well, as 

 the constant currents of water carry an abundant supply of the 

 minute organisms on which they feed. In such places it is not 

 uncommon to find five or six different species «»t ascidians attached 

 to the under side of the same stone. Sometimes several forms of 

 Compound Ascidians may be found attached to an individual of one 

 of the larger Simple Ascidians (Fig. 130). 



