that such constantly solitary Salpæ did not belong to species distinct from those united in chains, however dissimilar (and they are so dissimilar usually, as to appear even generically distinct), but were either the parents or the progeny, as the case might be, of the aggregate forms; that chained Salpæ did not produce chained Salpæ but solitary Salpæ which, in their turn, did not produce solitary beings, but chained. Consequently, as Chamisso graphically observes, 'a Salpa mother is not like its daughter or its own mother, but resembles its sister, its grandaughter, and its grandmother.'"
More recent researches have fully confirmed the correctness of these observations, strange as they at first appeared. Nor are the facts so singular as they were then believed to be; for the same law (now known as that of the Alternation of Generations), has been found to prevail extensively in the Medusæ and Hydroid Polypes.
One or more species of this genus have been at various times observed in the seas which wash the British coasts; and the first detection of the genus we owe to the eminent geologist, Dr. McCulloch. His graphic description of the discovery is so interesting, that I shall give it with a slight abridgement, though it repeats some details already mentioned. The species was probably Salpa runcinata.
"Some marine animals occur in these seas which remain still unrecorded in the catalogue of British zoology. Among these, indeed, it is probable that a few will be found still undescribed by naturalists, since fresh additions are even yet occasionally made to our catalogue of these ob-
- Brit. Moll. i. 47.