OBSERVATIONS ON POLYZOA. 221 



Arethusa, squirming in the perigastric cavity, and tossing 

 the stomach of the polypide about, as if it had been a play- 

 thing. They certainly, in this species, evinced sufficient 

 power to open a passage through the thin membrane of the 

 polypide, although such did not seem to be their object 

 at the time. 



No orifices for the expulsion of the ova have been as yet 

 positively demonstrated. Meyen chronicles the escape of 

 the eggs of Alcyonella (Plumatella) stagnorum from an 

 opening in the vicinity of the anus.* But this is, proba- 

 bly, erroneous, since, as observed by Mr. Hancock, "the 

 great size of the egg forbids the possibility of its escape 

 without the destruction of the polypide." 



From the preceding account it may be seen that there 

 are four localities, all within the ccenoecium, devoted to the 

 function of reproduction. These are, the ovary on the dor- 

 sal side of the orifice ; the free part of the endocyst of the 

 cell on the abdominal side, bringing forth true buds ; the 

 attached portion lower down, giving birth only to fixed 

 statoblasts; and the funiculus, generating spermatozoa and 

 free statoblasts. The true buds of Fredericella and Pluma- 

 tella are numerous, although only one usually matures and 

 prolongs the stem: when two or three mature, at the same 

 time, the lateral branches are produced. These buds grow 

 slowly, forming the ordinary tubular cells. In some varie- 

 ties of Plumatella, however, the buds mature more rapidly 

 and in greater numbers, while the branch assumes a lobe- 

 like form, the polypides, with the cells but half developed, 

 crowding the upper surface. This mode of formation, 

 which is only a variation of the species in Plumatella, is 

 of generic value in Pectinatella, where the polypides are 

 invariably arranged upon lobiform branches. In Cristatel- 

 la the true buds are more numerous than in any other 

 genus, and they mature until the ccenoecium is full grown. 



The gradual increase in the number of the buds, that 

 reach maturity, coincides with the decrease in the tough- 

 ness of the ectocyst, and its final obliteration in the higher 



*Meyen. Isis. 1828, p. 1228. 



essex inst. proceed, iv. cc. March, 1866. 



