MISCELLANEOUS. 65 



§ 5. Avenella fusca. — Vol. I. Plate XII. Fig. 11. — In the pre- 

 ceding volume we have seen that among the ascidian zoophytes there are 

 two which sometimes bear straggling single cells, with their animals on 

 the inorganic parts. These are the Valkeria citscuta and Boiverbankia 

 repens. 



The hydra of the former is provided with eight tentacula, that of the 

 latter with ten. 



In certain respects the subject of the present paragraph admits of 

 being compared with them, in as far as concerns the polyparium, if such 

 can be said to belong to it. 



This product, the Avenella, which may be held a provisional name, 

 occurs as a parasite, either on other zoophytes, or on slothful animals, such 

 as that species of crab called the Hyas araneus. It is commonly very 

 much matted and interwoven, and intricately confused with spurious vege- 

 tation. On the extrication of short single specimens, each is discovered 

 to consist of several cells, perhaps six or seven, set at irregular intervals 

 on a slender flexible stalk, not in the same line however, but rather around 

 the circumference. 



The cell is towards the sixteenth part of an inch long, either a straight 

 or a bent cylinder, curving even considerably more than any of the speci- 

 mens represented. On the whole, it bears some resemblance to a grain of 

 com.— Vol. I. Plate XII. fig. 11. 



An ascidian hydra inhabits the cell, protruding from 18 to 20 long 

 ciliated tentacula, disposed in circular arrangement, much in form of a 

 funnel. These cilia are not easily seen. The animal is quick and lively, 

 rising cautiously to view, and retreating abruptly below. 



The whole product is of a brown or horn colour. It is rare. I have 

 obtained it thrice. On the second occasion, after a long interval, there 

 might be 100 cells dispersed among various specimens. On the third oc- 

 casion, several hundred cells were dispersed amidst tufts. 



Vol. I. Plate XII. Fig. 11. — Avenella fusca, enlarged. 



VOL. II. 



