MONOECIOUS MOLLUSCA. 343 



These views of Savigny have been not only not confirmed, 

 but tliey are disproved by the observations of Milne-Edwards 

 and of Sir John G. Dalyell, who find that the embryo and 

 larva of the compound Tunicata is as simple as that of the 

 single Ascidia, and so like it in structure, form, and deport- 

 ment, as to need no further description. The character of 

 the compound species depends on the law which regulates 

 the evolution of its embryo, and this is carried out by the 

 successive growth of germs or buds, which Nature has 

 ordained shall be a necessary sequence of its own life. 

 Becoming fixed to their extraneous site, the embryos are 

 soon observed to shoot out, from one or more determinate 

 points in their base, short papillae, or, as in the social tribe, a 

 lengthened stolon, which, by an imperceptible growth, soon 

 becomes a perfect organism in all respects like unto its egg- 

 parent ; and no sooner has it attained individuality than it 

 again sends forth its pullulating radicles, each to become 

 like the original, and each fit, in due time, either to augment 

 the population of the mass to which it is associated, and of 

 which it is a native ; or to propagate its species by the 

 engendering of an ovarian egg and tadpole larva.* There is 

 nothing peculiar in this mode of increase. The polype that 

 lives in a compound mass, or which sends up new poly- 

 piferous offsets from its base, and the plant which overruns 

 a soil with shoots pushed out on all sides of it, afford analo- 

 gous examples. 



I have now a rarer and more singular mode of propagation 

 to bring under your notice, and yet its anomalous course 

 need not shake your faith in its reality. The student of 

 these lower tribes soon becomes familiar with miracles ; and 

 uncommonness, or even want of analogy with other pheno- 

 mena, is no bar with him to the fair discussion and reception 

 of a fact. 



" Multa tegit sacro involucre natura ; neque ullis 

 Fas est scire quidem mortalibus omnia : multa 

 Admirare modo, necnon venerare ; neque ilia 

 Inquires, quse sunt arcanis proxima." 



The Biphores or Salpae (Fig. 43, p. 49), constitute one 

 of the most remarkable and abundant genera of compound 

 Tunicata in temperate and tropical seas, where they are 

 seen swimming or floating about, during the calms that 

 soothe the glistening surface, in crystalline masses of many 



* Milne-Edwards, sur les Ascid. Comp. 41, &c. ; Dalyell's Rare and 

 Remarkable Anim. Scot. ii. 164. 



