610 RECORD OF CURRENT RESEARCHES RELATING TO 



a septum from tho tail wLicb is purely protoplasmic ; it originates from 

 a nucleolus which is similarly refringent. On becoming attached to the 

 ovimi its central part contracts into a lumj) on which the head rests, 

 and the whole becomes covered by a membrane proceeding from the 

 side of the head. After segmentation the mass is converted into a 

 gastrula by invagination ; the gastrula-mouth closes and the segmen- 

 tation cavity disappears, and a ring-shaped depression appears in 

 front enclosing a space which becomes the wall of the future cystid. 

 Three layers are now present in the body ; tho outer layer, the tunica 

 muscularis, and the entoderm. The cells of the ring or " cap " 

 lengthen and become connected with fibres ; the polypides which 

 develop within it j)ush out the external membrane round them ; the 

 cilia of this membrane cease moving, and its layers of cells unite and 

 then break up into long homogeneous separate cells ; in many cases 

 this mass of cells forms a long process at the side of the cystid, and 

 sometimes even increases in size ; its further development was not 

 observed, but after a time it was seen to be absorbed into the cystid ; 

 it probably represents the stolon of marine Polyzoa. 



The structure taken for an ooecium by Nitsche and Metschnikoff 

 appears to be an extension of the ovarian membrane, with which it 

 corresponds in position, in its unilaminar structure, and in containing 

 embryos in stages too early for their emergence. By the formation 

 of the embryo, the polypides adjoining it appear to be destroyed and to 

 form the " brown bodies " ; through the openings left by their dis- 

 appearance the embryo issues forth ; the statohlast originates in the 

 same Avay, and also at the expense of the aborted polypides. The 

 digestive canal is developed from the internal layer of the capsule 

 which encloses the embryo, and not from a specially separated group 

 of cells, as Hatschek states. 



With regard to Cristatella mucedo, the author gives the following 

 preliminary account of the development : — 



The cystid consists, as in Alcyonella, of an ectoderm, a median 

 layer (the tunica muscularis), and an entoderm. Thus Hatschek must 

 be wrong when he names the inner layer of the bud, mesoderm ; and 

 his description of the budding is inexplicable by comparison with the 

 above-mentioned details, though these may perhaps correspond with 

 his second, unknown, process of budding. The bud develops by a 

 thickening of the ectoderm into which the entodermic cells are 

 pushed ; there is no indentation of the former. The tunica muscu- 

 laris is very early formed ; the cavity of the tentacle-sheath is 

 separated later from the alimentary canal, and the lophophore is 

 formed by an invagination into this tentacle-sheath. The later deve- 

 lopment of the buds corresponds with that described by Nitsche in 

 Alcyonella. The statoblasts consist of a uniform granular mass, 

 covered with the cylindrical cells of the ectoderm, under which cells 

 lies a layer of nuclei ; the layers increase in number, the tunica 

 muscularis appearing first ; the entoderm was hid by the opacity of 

 the central mass. 



The well-known concerted movements of the colony are explained 

 by the structure of the common base, which contains suckers formed by 



