Invertebrate Animals of the Western Coast of France. 31 



canals already mentioned. Living thus as parasites, they yet 

 perform important uses in the ceconomy of the polypary, since, 

 charged with the process of reproduction, they appear specially 

 destined to ensure the establishment of new colonies. 



M. Quatrefages has seen the Synhydrce propagate by three 

 very distinct methods. In the one case the young individual 

 proceeds from a bud formed upon the surface of the common ba- 

 silar tissue, and which is developed nearly in the same manner as 

 the reproductive gemmules of the Hydras and Sertularias ; in 

 another, ovules like those of the sponge arise in this common 

 tissue ; and lastly, reproductive bodies {bulbilli) are met with upon 

 the free portion of the polyps, which cannot be likened either 

 to gemmae or ovules, for they grow by an extension of their tis- 

 sue like the first, and, like the second, separate completely from 

 the parent stem before becoming developed into new individuals. 

 The reproductive gemmules serve to increase the population of 

 the colony in the midst of which they are formed ; the ovules re- 

 main probably buried in the basilar tissue after the winter has 

 destroyed the polyps covering it, and produce other Hydras on 

 the following spring ; while lastly the bulbilli, becoming detached 

 and borne afar by the currents, fix themselves at length in some 

 appropriate spot, develope, and multiplying again by gemmae, 

 found a new colony, in a manner similar to that by which the 

 compound Ascidia disperse to a distance their sessile societies by 

 means of locomotive larva?. These bulbilli are exclusively pro- 

 duced by the astomatous polyps, around the summit of which 

 they are grouped, the polyps provided with a mouth appearing not 

 to participate in any degree in the work of generation. The first 

 then are the reproductive, the second the nutrition-serving indi- 

 viduals, and both exhibit corresponding differences of structure. 

 The tentacles of the reproductive polyps are represented only by 

 tubercles, and their digestive cavity resembles that of a polyp 

 whose development is not completed and the stomachic cavity not 

 yet open externally. Arrested as regards the functions of nutri- 

 tion and of animal life, all the energies of their organism seem 

 concentrated upon the exercise of the generative power ; for there 

 is nothing that could lead us to suppose that the nutritory indi- 

 viduals are males, and the astomatous females ; but rather that 

 the two great physiological acts, the one necessary to the preser- 

 vation of individual life, and the other destined to perpetuate the 

 existence of the species, are here exhibited under a separate and 

 independent form in the same community. This mode of pro- 

 pagation by bulbilli in the Synhydrce constitutes a form of repro- 

 duction not hitherto well determined to occur in the animal 

 kingdom, and we cannot therefore peruse the beautiful researches 

 of M. Quatrefages without feeling their interest no less as bear- 



