220 



HYATT. 



nuclei of the cells are of large size and in due time are con- 

 verted into spermatozoa. These have been observed swim- 

 ming freely in the perigastric cavity into which the full 

 grown ova are, also, discharged from the ovary. 



After the segmentation of the vitellus, the egg appears 

 as a hollow oval body clothed externally with cilia, and it 

 is at this period that most observers have seen and des- 

 cribed its peculiarities. 



Mr. Albany Hancock, although confounding it with a 

 statoblast which he supposed to be an egg, speaks of one, 

 an undoubted ovum, which, he observed forcing its way 

 through the closed orifice of the cell, rending and destroying 

 the parent polypide in its course.* 



I have, also, seen them during this stage in Plumatella 



tral cavity, which as jet does not open externally. When liberated from 

 the outer membrane of the ovum, which still confines it, it swims ac- 

 tively through the surrounding water by the aid of the cilia with which 

 it is invested. 



As development proceeds, we find the ciliated embryo while still 

 confined within the coverings of the egg, presenting in some part of 

 its surface an opening, which leads into the central cavity ; and through 

 this opening an unciliated, hernia-like sac is capable of being protrud- 

 ed by a process of evagination. The unciliated protrusible portion 

 would seem to have been derived by a separation from the walls of 

 the central cavity, and appears therefore to originate by a process of 

 unlinmg, a true chorization. 



Towards the opening, which leads from without into the central 

 cavity, the chorization is incomplete, the membrane as it separates 

 being here still held to the walls of the cavity by irregular transverse 

 bands: these bands check the entire evagination of the membrane, but 

 after a time they disappear, and then the unlining and evagination are 

 perfect. In the interior of the protrusible portion, and before the dis- 

 appearance of the transverse bands, a polypide is developed." The 

 further development of this polypide. as described by Prof. Allman, 

 does not difl'er materially from those produced from the regular buds 

 of the adult cells. 



The same authority thus describes the testicle of Alcyonella (Plu- 

 matella) fungosa on page 32 of the work above quoted. 



'•The testicle is composed of a mass of spherical cells, each of which 

 contains within it numerous secondary cells, "vesicles of evolution." 

 The visible contents of the vesicles of evolution consist, at first, of 

 nothing more than a well-defined spherical nucleus, and this is subse- 

 quently transformed into a spermatozoal filament, which fin all}' escap- 

 es by the rupture of the containing cells. The spermatozoal filaments, 

 in this genus, are simple vibrioid bodies without any terminal enlarge- 

 ment." 



*Haxcock. Op. cit. p. 18G, note. 



