TEE COMPOUND ASCIDIANS. 253 



surface of the rock, now depending from it in icicle-like projections. These are compound Ascidians. 

 A tangle or broad-leaved fucus, torn from its rocky bed, or gathered on the sands where the waves 

 have cast it after storms, will show us similar bodies, mostly star-figured, investing their stalks, 

 winding among the intricacies of its roots, or clothing with a glairy coat the expanse of its foliated 

 extremities. If we keep some of these bodies alive in a vessel of sea water, we find them lie there as 

 apathetic as sponges, giving few signs of vitality beyond the slightly pouting out of tube-like mem- 

 branes around apertures which become visible on their surfaces, though a closer and microscopic 

 examination will show us currents in active motion in the water around those apertures, streams 

 ejected and whirlpools rushing in, indicating that, however torpid the creature may externally appear, 

 all the machinery of life, the respiratory wheels and circulatory pumps, are hard at work in its inmost 

 recesses. In the course of our examination, especially if we cut up the mass, we find that it is not a 

 single animal which lies before us, but a commonwealth of beings, bound together by common and 

 vital ties. Each star is a family, each group of stars a community. Individuals are linked together 

 in systems, systems combined into masses. Each member of the commonwealth has its own peculiar 

 duties, but shares also in operations which relate to the interest and well-being of the mass. Anatomi- 

 cal investigation shows us the details of these curious structures and arrangements, beautiful as Avise. 

 Indeed, few bodies among the lower forms of animal life exhibit such exquisite and kaleidoscopic 

 figures as those which we see displayed in combinations of the compound Ascidians. 



The merit of first understanding and interpreting the true nature of these curious bodies is due 

 to Jules Cesar Savigny, an illustrious French naturalist, whose zeal in the cause of minute investiga- 

 tion eventually deprived him of sight, and the world of many profound and philosophical researches. 



Before Savigny's time the BotryllidaB had been confounded with Polypes, and regarded as 

 forms of the genus Alcyonium, to which, indeed, the masses bore a striking resemblance. The 

 earliest distinct figures of these forms appeared in the Philosophical Transactions for 1757, where 

 they were published by Schlosser ; and in 1758, that curious observer Borlase gave descriptions 

 sufficiently graphic, and rude but unmistakable figures, of several species, in his interesting folio 011 

 " The Natural History of Cornwall." The first naturalist who indicated their compound nature, and 

 held forth a clue to their true affinities, was the famous botanist Gaertner, whose zoological observa- 

 tions on marine animals, communicated to and published by Pallas in 1774, are of the highest degree 

 of merit. Gaertner, however, did not follow up his inquiries in these bodies, though to him we owe 

 the generic groups Botryllus and Distomus. The Italian naturalist, Eenieri, in 1793, had a similar 

 obscure perception of their affinities. 



The memoirs of Savigny, published in 1816, however, threw entirely new and unanticipated 

 light on their nature. He showed that they were essentially Ascidians, differing from the simple 

 forms only in being united into more or less complicated systems. The researches of Milne-Edwards 

 "On the Compound Ascidians of the Channel," read before the Institute of France, 1839, have fully 

 confirmed those of Savigny, and have also greatly extended our knowledge of these creatures. The 

 figures given by both these naturalists are among the most beautiful and minutely accurate that have 

 ever illustrated and adorned natural history essays. (Forbes). 



Genus Botryllus. The animals of this genus offer no distinction between thorax and abdomen ; 

 their organs of digestion, <fec., occupy the thoracic cavity, forming an ovoid mass. The branchial 

 orifices are simple, ranged horizontally round a common cloaca, in groups of simple stars. There are 

 ten species found in the United States and Europe. 



Genus Didemnium* The test is coriaceous, polymorphous, sessile and incrusting ; the systems 

 numerous, compressed, without central cavities ; the individuals are scattered ; the abdomen is peduncu- 

 late, and the ovary is placed by the side of the intestinal loop. It is found in Europe. 



Genus Eucodum.\ The test is gelatinous, but in other respects closely resembling Didemnium, save 

 that the animals are sometimes arranged in fives (quincuncially). Its distribution is in the European seas. 



Genus Leptoclinum.^ The test is thin, gelatinous or coriaceous and incrusting. The individuals 

 are irregularly grouped round common cavities. Six British species are found on roots of Laminaria. 

 The colour is yellowish-white, variegated with blue. 



* Greek, dis, double ; demnia, a bed. + Greek, eu koilos, much excavated, 



i Greek, leptos, thin ; Mine, a couch. 



