266 REPORT ON THE PENNATULIDA. 



All the four Oban specimens in which the lower end of the rachis is 

 perfect, prove on examination to be females, so that we have had no 

 opportunity of investigating the development and I'elations of the 

 male organs. We regret this the more because the descriptions we 

 possess of these organs are not in all respects satisfactory. 



Young ova in the earlier stages of development are only found at 

 the very bottom of the rachis, or, at any rate, only where the polypes 

 are very immature ; they are also far more abundant in the ventral 

 than the dorsal half of the rachis, if, indeed, they are not confined to 

 the former. Mature ova — i.e., eggs which have reached their full size 

 and become detached from their stalks, are found extending much 

 higher up the rachis, and may occur in the body-cavities of fully- 

 developed polypes. 



If it is borne in mind that each leaf commences its existence at the 

 bottom of the rachis, and is gradually forced upwards by the successive 

 development of new leaves below it, it will be seen that each leaf in 

 the early stages of its existence has fully-developed reproductive organs, 

 but no organs for digestion of food or capture of prey ; and that in the 

 later stages of its life it loses its reproductive organs and develops 

 prehensile and digestive organs. In other words, the two great functions 

 of nutrition and reproduction, which are carried on simultaneously in 

 the polypes of Funiniliiia and Pejinatula, occupy in Virgularia different 

 phases of the life-histoi-y of the polypes, and strangely enough the 

 reproductive phase precedes the nutritive ; the polypes develop repro- 

 ductive organs and products while they are yet unable to catch or 

 digest food for themselves, and by the time they have acquired organs 

 for these latter purposes the reproductive organs have disappeared. 



In presenting this separation of their life-history into two distinct 

 chapters, as it were, the polypes of Virgularia are less primitive, and 

 more specialised, than those of either of the other genera with which 

 we have been dealing. 



None of the ova that we have examined from the Oban specimens 

 have even commenced to develop, so that we can give no account of 

 the processes of development from our own observations. Dalyell, 

 who kept Virgularia in captivity for some naonths, informs us * that 

 during May and June he found numbers of eggs at the bottoms of the 

 glasses in which he kept his specimens ; that from these eggs larvae in 

 the form of free-swimming ciliated planulas were developed, which after 

 a time attached themselves by oiae end and produced tentacles, a 

 stomach, and four septa. • He kept these young specimens for a month 

 without their undergoing any further change. 



By means of fertilised ova and the free-swimming larvae to which 

 they give rise new colonies of Virgularia are started. Increase in size 

 of the colony, when once started, is effected by the formation of leaves 

 one below another, as already noticed. The actual process of formation 



* Sir John Graham Dalyell : " Kara and Remarkable Animals of Scotland," 

 vol. ii., p. 188, 1848. 



