61 ANTHOZOA. 



gether by their outer surface, and are surrounded by a sort of sheath, 

 no external buds are formed, but the ovules make their escape into the 

 internal cavity of their parent. Hence the distinguished zoologist 

 whose memoir we quote is led to infer that, on the one hand, the 

 mechanical obstacles to be encountered, and, on the other, the excite- 

 ment occasioned by the contact of the surrounding element determine 

 this difference of procedure, and that the membrane which performs 

 the functions of an ovary produces indifferently either ova or gemmae, 

 according as it finds less resistance or is more stimulated upon the in- 

 side or the outside of the abdominal walls. 



(140.) Prom the above details it becomes easy to explain how a 

 single polyp by its reproductive powers can form the complicated mass 

 of the compound polypary of the Alcyonidae, as well as the means 

 whereby an organic continuity is established between all the individuals 

 of the community; also how the abdominal cavity of the primitive 

 zoophyte becomes common to all the young ones that sprout from it ; 

 in short, how the little beings thus united together rather resemble a 

 multiple animal than an assemblage of distinct individuals. But with 

 the advance of age this intimate union gradually ceases. The com- 

 munication between the abdominal cavities of the different polyps, 

 whose basal portions reach as far as the foot of the polypary, is first 

 of all interrupted by the ova with which the lower part of these 

 cavities becomes filled (fig. 2ft, 3) ; and subsequently, by the pressure of 

 the surrounding parts, the wall becomes confused, and all communica- 

 tion between the polyp whose abdominal tube is thus obliterated and 

 the polyp from which it sprung is intercepted. The polypary, instead 

 of resembling a tree, all the flowers of which hold together and com- 

 municate by common parts, may now be compared to a bouquet made 

 by cutting off the more or less branched twigs of a plant and collecting 

 them in a bundle. The different groups of polyps united in the same 

 polypary become thus independent of the neighbouring groups, and, 

 as may readily be conceived, in time each polyp can become indi- 

 vidualized. 



(141.) In the Alcyons properly so called, a vascular system is very 

 distinctly developed ; and in Alcyonium stellatum more especially, M. 

 Milne-Edwards was able to study it with facility. In this species 

 (fig. 28, l) he was enabled to detect, upon the parietes of the abdominal 

 cavity of the polyp, a variable number of minute apertures irregularly 

 dispersed, which are in immediate communication with a system of 

 capillary canals that traverse in all directions the spongy portion of 

 the polypary, formed by the external tunic of its component animals ; 

 for in Alcyonium it is very easily seen that while the internal tunic 

 lines the abdominal cavity of the polyp, the external layer, instead of 

 being confounded with the former, as in the protractile portion of the 

 animal, becomes perfectly distinct from it where it begins to enter into 



