POLYZOA. 605 



(in the " Ectoproctous " Poly zoo), but sometimes within it (in the 

 " Entoproctous " Poly zoo). The alimentary canal is moored to 

 the body-wall by muscular bands, those springing from the bottom 

 of the cell serving to retract the polypide within its chamber, 

 while the protrusion of the tentaculated anterior extremity is 

 effected by muscular fasciculi which run in a circular manner in 

 the wall of the cell. 



Each polypide possesses a single nervous ganglion (fig. 450, g), 

 which is placed upon one side of the gullet, between it and the anal 

 aperture. The different polypides may also be connected together 

 by a remarkable organic structure, which was at one time believed 

 to be of a nervous nature, and was termed the " colonial nervous 

 system," but which is now generally spoken of as the " endosarc." 

 This singular connective system, by which the different polypides 

 of the colony are organically united, commences as a peculiar cel- 

 lular cord, the "funiculus" (fig. 450, z), which stretches from the 

 base of the stomach to the bottom of the zocecium, and upon which 

 the testis is developed. At the point where the funiculus is fixed 

 to the bottom of the cell, a perforation in the ectocyst exists, and 

 filaments of the funiculus thus either pass into adjacent polypides, 

 or become connected with a common branched fibre which runs 

 through the stolons of the colony (as in Boiverbankia). In many 

 cases the endosarcal cords give off branching fibres, and they have 

 a general likeness to a nervous system. Histologically, however, 

 the endosarc does not consist of nervous elements, and it may be 

 regarded as a kind of ccenosarcal structure, which is largely con- 

 nected with the production of the generative elements, and from 

 which, possibly, the polypides are produced by gemmation. 



The polypide of the Polyzoa is generally hermaphrodite, the ovary 

 (fig. 450, 0) being usually situated near the summit of the cell, 

 attached to the inner surface of the endocyst, while the testis (x) is 

 placed at the bottom of the cell, and is attached to the "funiculus." 

 The generative elements are usually set free into the perigastric 

 space, the ova being thus fecundated within the body-cavity of the 

 parent polypide. The fertilised ova may pass into special dilata- 

 tions of the cell (" ovicells "), or the embryos may be hatched 

 within the perivisceral cavity of the parent. 



The embryo is, to begin with, ciliated and freely locomotive, but 

 ultimately fixes itself, and, except in Loxosoma, begins to produce a 

 colony by means of budding. The new buds are usually produced 

 from the dorsal wall of the polypide, or from its sides, or sometimes 

 from its anterior extremity. Fission, so common among the Ccel- 

 enterates, has never been noticed to occur. The ultimate form of 

 the polyzoary depends upon the precise method in which the new 

 buds are developed. The separate polypides of the colony are ap- 



