ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 937 



lamella of the tube wHcli carries them, and have the general form of an 

 urn. The walls are formed of two layers, the outer of which is delicate, 

 chitinous and structureless ; this is the ectocyst ; the endocyst is cellular, 

 and thickest in the median region. The term spherules is applied to 

 two rounded masses which are placed symmetrically on the sides of the 

 zooecia ; they consist of a central cavity, which is filled with liquid, and 

 occupies the greater part of the spherule, and of a resisting wall formed 

 by the ectocyst and endocyst. Their function appears to be that of pro- 

 tective organs, acting passively by preventing the compression of the 

 zooecium by the Chsetopterus. Morphologically, these bodies appear to 

 be modified individuals. The colony may be considered as formed of 

 a series of differentiated segments placed one behind the other ; the 

 polypide has from 12 to 14 tentacles, and a gizzard.' 



Fresh-water Bryozoa.* — Herr F. Braem has been led to disbelieve 

 in the theory that a new polypide may arise at any point of the body- 

 wall by the invagination of its two layers, for he has always found that 

 the formation of young buds is connected with the pre-esistence of older 

 ones. He thinks he can show that no bud arises ia the colony which 

 cannot be referred to the embryonic cell-material of an older bud- 

 rudiment. If we take a bud a at an early stage, when it merely 

 represents a two-layered sac, we find it to give rise to a daughter-bud b ; 

 as these become separated from one another a second bud b' appears 

 between them ; and this may be repeated as long as the primary 

 bud is provided with material which is capable of division. Similarly 

 the daughter-buds may give rise to other buds, until at last the youngest 

 individuals are no longer capable of germination. 



The inner layer of the bud becomes fashioned into the ectoderm, 

 while the outer forms the inner epithelium of the wall of the cystid ; 

 the cells of the latter are partly differentiated into the muscular tissue 

 of the integument and of the gut, and partly give rise to the retractor 

 and folding muscles, and to long unicellular filaments which connect 

 the polypid and cystid. The difference in the rapidity with which the 

 bud-generations follow one another is the cause of the delicate branched 

 colonies like those of Fredericella and Plumatella fruticosa on the one 

 hand, and the more compact colonies of Alcyonella on the other. Further 

 differences may, at last, result in the formation of a Cristatella. This 

 last is to be regarded as a colony of Phylactoloemata with creeping 

 individuals which have become so approximated to one another that 

 their cystids have fused laterally; the sum of the basal parts of the 

 cystids becomes the foot, and that of the dorsal pieces, with the orifices, 

 the upper covering of the apparently unjointed colony. The metamor- 

 phosed lateral parts appear to be septa in the interior of the common 

 body-space, and there are consequently only radial septa, for those 

 which have been described as being perpendicular to these do not exist. 

 The manner in which the buds follow one another in Cristatella is 

 essentially the same as in other Lophopoda. 



In all the Phylactoloemata observed by the author the statoblast 

 gives rise to a single primary individual, which forms the stock by 

 budding in the same way as the younger branches are developed later 

 on. The funiculus of Cristatella arises at the time when the gastric 

 space is cut off in the lower part of the saccular primary knob by the 



* Zool. Anzeig., xi. (1888) pp. 503-9, 533-9. 



