POLYPIFERA. 



27 



or less distinct from the animals themselves ; 

 but in the Zoophyte we are speaking of a 

 superficial examination is sufficient to con- 

 vince any one that these cells are in reality 

 continuations of the bodies of the polypes 

 themselves. The tubes which form the trunk 

 ( fig. 30, c), are in all respects similar to 

 the free portion of the animal which is 

 situated beneath its alimentary canal, and no 

 line of organic separation can be traced di- 

 viding one from the other. It is not, there- 

 fore, into polypiferous cells that these little 

 animals retire in the manner of Serpulae or 

 Dentalia, but they recede into themselves by 

 a kind of invaeination of their own bodies, the 

 polypary, which seems to contain them, being 

 simply a mass formed by an assemblage of the 

 basal portion of all the aggregated zoophytes. 

 When the polypes extend themselves, their 

 mouths may frequently be seen to open and 

 admit the surrounding water. This fluid, 

 together with the alimentary materials sus- 

 pended in it, penetrate into the digestive sac- 

 culus, and afterwards pass into the great ab- 

 dominal cavity, whence they are conveyed 

 even into the tentacula by the eight canals 

 placed around the alimentary tube. It thus 

 results that the thin and diversely folded 

 membrane, of which the bodies of these 

 animals are formed, is everywhere bathed, 

 both within and without, with the materials 

 for respiration, and that all its internal surface 

 receives the contact of the alimentary sub- 

 stances after their elaboration in the digestive 

 sacculus. M. Milne Edwards likewise thought 

 he perceived something like a circulation in 

 canals contained in the parietes of the body ; 

 but of this he was uncertain. 



Nutrition of Alcyonide. It is very gene- 

 rally admitted that in the case of these ag- 

 gregated zoophytes the nutritious materials 

 taken by one of the animals is shared with 

 the neighbouring polypes; and this fact M. 

 Milne Edwards has established beyond the 

 possibility of doubt, as well as the manner in 

 which it is effected. In an expanded Alcyo- 

 nide he introduced, by means of a fine pointed 

 glass tube, a coloured fluid into the abdominal 

 cavity of one of the polypes, and immediately 

 the injected material diffused itself, not only 

 throughout the tubiform body of the indivi- 

 dual so treated, but passed at the same time 

 into the neighbouring polypes. The passages 

 by which this communication is established 

 are easy to discover, by making a longitudinal 

 section of the body of the Alcyonide. It is 

 then seen that some of these animals, whose 

 tube-like bodies are prolonged deeply into 

 the common mass, there terminate by cuh de 

 sncs, whilst others are not continued beyond 

 the point where they join their congeners ; 

 and in this case their bodies are found to be 

 continuous witli that of a larger polype, the 



This condition of their nutritive system 

 arises from the mode of their development by 



Fig. 32. 



Alcyvnid'mm elegans. 



A, one of the brandies laid open to show the 

 communication between the abdominal cavity of 

 the principal polype and the interior of the young 

 ones that spring from it ; the openings thus formed, 

 (e, e, e,) are situated in the course of the longitudinal 

 folds, which perform the office of ovaries, a, ten- 

 tacles of the principal polype ; b, c, d, the young 

 polypes in progressive stages of development. 



B, the lower portion of one of the longitudinal folds 

 detached, showing the manner in which the ova 

 are developed in it. (.After Milne Edwards.) 



gemmiparous reproduction, which takes place 

 as follows. A tubercle makes its appearance 

 upon the surface of the body of an adult po- 

 lype, which seems at first to be only a little 

 coecal appendage developed from its parietes, 

 its extremity being without any opening and 

 the cavity in its interior communicating freely 

 with the abdominal cavity of the individual 

 from which it was developed. Shortly, how- 

 ever, as its development proceeds, a mouth 

 and its surrounding tentacula make their ap- 

 pearance, an alimentary cavity becomes ap- 

 parent, and the newly formed animal becomes, 

 both in shape and size, exactly like the indi- 

 vidual from which it sprouted. 



This mode of reproduction, Milne Ed- 

 wards remarks, does not occur at any point 

 of the tegumentary surface. The reproduc- 

 tive gemmae are only formed along the course 

 of the membranous lamellae already men- 

 tioned, and the inferior opening of the body 

 of the new polype is always so situated as to 

 intercept one of the longitudinal folds in the 

 abdominal cavity of the parent animal. 



But the mode of reproduction by gemmae 



basal portion of which descends lower down is not the only one by which the Alcyonides 



(fig. 32). The abdominal cavities of these 

 animals are thus united, so as to constitute a 

 kind of branched tube, possessed of as many 

 heads and mouths as there are polypes de- 

 rived from it. 



are multiplied. They produce also ova, or 

 gemmules, by means of which their sedentary 

 race may be disseminated ; and it is remark- 

 able that the same parts which give birth to 

 the gemmae above described perform likewise 



