40 GEMMATION. 



place after the destruction of the soft parts of the polyzoon has afforded to them a mode 

 of egress through the orifice of the cell. 



In two species of fresh-water Polyzoa, Plumatella emarginata and Alcyonella Benedeni, I 

 have observed, besides the ordinary statoblasts, another kind which is characterised by some 

 peculiarities. In both these Polyzoa the cells may be observed towards the end of summer 

 loaded with statoblasts which lie loose within them. These are the ordinary ones, and, in 

 the two species of Polyzoa now under consideration, are of an elongated oval figure, with a 

 largely developed annulus which overlaps a considerable portion of the disc (PI. IV, figs. 7 — 9 ; 

 VII, figs. 7, 8). But, besides these bodies, others (PI. IV, fig. 10; VII, fig. 9) may be 

 observed which never lie loose in the cell, but are invariably attached to the internal 

 surface of the walls, to which they adhere by means of a peculiar cement in which no 

 trace of structure can be detected. These differ also from the unattached statoblasts in 

 shape, being much broader in proportion to their length, while the annulus is exceed- 

 ingly narrow and presents but slight traces of that highly developed cellular structure 

 so remarkable in the others. After the decay of the ccenoecium many of these attached 

 statoblasts may be seen adherent to the stone or other body on which the specimen had 

 developed itself, and to which they are now connected in lines (PI. VII, figs. 5, 10) through 

 the medium of a portion of the old cell in which they had been produced. I am unable to 

 state whether the origin and destination of the last-described bodies is similar to that of the 

 others, and I have not succeeded in witnessing the escape from them of the young. 



In Alcyonella func/osa and Lophopus crystallinus I have also occasionally seen bodies, 

 which differ from the ordinary statoblasts of these Polyzoa by the possession of a regular 

 elliptical aperture in the centre of their more convex face. They were always empty, and of 

 their nature I have not been able to form any conclusion ; they are most probably abnormal. 



The general structure and development of the statoblasts being now understood, the 

 important question at once suggests itself, what is the true import of these bodies .' All that 

 we have seen of them is manifestly in accordance with the nature of a bud. The invariable 

 absence of germinal vesicle and germinal spot, and their never exhibiting the phenomena of 

 yelk-cleavage, independently of the conclusive fact that true ova and ovary occur elsewhere in 

 the same individual, are quite decisive against their being eggs. We must then look upon 

 them as yemma peculiarly encysted and distined to remain for a period in a quiescent or 

 pupa-like state. It was for this reason, therefore, that I proposed for them the name of 

 statoblasts.* 



How far the statoblasts of the Polyzoa admit of comparison with the " winter ova" of the 

 Botiferce and the epMppia of Daphnia remains yet to be determined. Huxley has studied the 

 production of " winter ova" in Lacinularia, and, though he has shown these bodies to be 

 derived from a portion of the ovary, he is yet of opinion that they must be regarded &s,ffemm(B.\ 

 He has carefully traced the early stages of their development in Lacinularia, and has shown 

 that their contents are at one period divided into two masses. Tlie reader will recollect that 

 a precisely similar condition is presented by the statoblasts of the Polyzoa at an early period 

 of their development ; in the Botiferce, however, the two masses appear to continue distinct, 

 while in the Polyzoa they are subsequently fused into a single mass. The recent researches 



* Srorilg, j3/\uar»)- f ' Quarterly Journal of Microscopical Science,' Oct., 1852. 



