186 LECTURE IX. 



was in the progress of developing two others. Dalyell obtained from 

 these a colony of eight larval " hydrae tubae." These were extremely 

 voracious ; they were fed with the flesh of mussels ; and in proportion 

 as they were fed was their power of converting their food into crea- 

 tures like themselves. By July 21st fifteen hydrae were propagated, 

 and ultimately a colony of eighty-three were obtained from the 

 individual insulated on the 23rd of April. It would seem that con- 

 finement tended to check the metamorphosis into the " oviparous 

 form," and favoured the gemmation of the polype individuals, or the 

 " typical form." At length, however, in the spring of a subsequent 

 year he observed the phenomena which he thus describes, in the 

 " Edinburgh Philosophical Journal" for 1836 : — 



*'Ikept a colony of these animals and their descendants during six 

 years ; numbers attained maturity ; they fed rapaciously ; grew and 

 bred, succeeding at all seasons of the year. But, in February and 

 March, the face or disc of some hydras is invested by a pendulous 

 flexible prolongation of an inverted conical form^ obliterating the 

 tentacula entirely. The apex being connected with the disc, this 

 pendulous mass extends two or three lines in the course of time, and 

 is gradually developed in twenty or thirty successive strata, gradually 

 broadering outwards. Wlien more mature, the vehement clasping of 

 extending arms at the extremity denotes that each stratum is an 

 animated being, which, after excessive struggling, is liberated, to 

 swim at large in the water. This also maybe associated with the 

 medusarige. It is considerably larger than the preceding, two lines in 

 diameter : of a whitish colour, tending to transparence. The body 

 resembles a flattened watch glass ; the margin dilating into from 

 five to twelve horizontal, broad, flattened lobes, each cleft half way 

 down the middle, and with a black glandular-looking speck in the 

 centre of the fork. A crest, resembling a quadrangular clustered 

 column, rises from the convex surface of the body, and four organs 

 may sometimes be observed on the same surface near its base. 

 Motion is accomplished in jerks or leaps, somewhat as by the Medusae 

 proper, from percussion of the lobes on the water, the crest being 

 downwards. Whether the pendulous mass or its individual parts be 

 contained in one common involucrum, or in many specific integu- 

 ments, is uncertain ; but each of the animals composing it comes 

 successively to maturity and departs. As the pendulous prominence 

 disappears, the vigour of the hydra is restored, and the tentacula, 

 liberated of the encumbrance, effecting temporary obliteration, resume 

 their natural form and functions. Weeks elapse in the course of this 

 process, and during survivance of the animals." So that here the 

 observations by Sars, of his Scyphistoma (1833), illustrated by 



