POLYPIFERA. 



29 



well described by Spix, and subsequently 

 more in detail by 'Milne Edwards in the paper 

 above referred to. The following is the re- 

 sult of Spix's observations. 



" The mouth is a small rounded aperture, 

 which is very dilatable, and communicates 

 immediately with the stomach. The mouth 

 is surrounded by eight tentacles, having a 

 papillary surface, and they appear to contain 

 internally a multitude of little air bubbles. 

 They are very sensible, for as soon as they 

 are touched they retract, and the animal re- 

 tires into its cell. 



" The polype is retained in its domicile by 

 a muscular membrane, which is very distinct 

 from the walls of the stomach, and is almost 

 cylindrical ; it descends from around the 

 mouth, and is fixed to the edges of the cell ; 

 it appears to form the tentacles and the sto- 

 mach, as in Actinia. The contraction and 

 extension of the polype is effected by this 

 membrane." 



For many days during which Spix watched 

 these polypes he observed little globular bodies 

 to ascend from beneath the stomach and issue 

 at the mouth. By pressing gently he saw 

 them glide as by a little orifice into the sto- 

 mach, and by the same proceeding he suc- 

 ceeded in pushing them under it. 



Having raised the muscular membrane at 

 the point where it is fixed to the polype, he 

 perceived at the bottom of the cell, and be- 

 neath the stomach, seven or eight globules 

 contained in a bent canal (ovary), placed in a 

 row. They gave to the canal the appearance 

 of a row of vesicles. The globules are round ; 

 those which are most developed red, each 

 enclosing a multitude of ova. 



" When the animal is drawn out of its shell, 

 by tearing the muscular membrane, the ovary 

 detaches itself from the stomach and remains 

 at the bottom of the cell. But there is an- 

 other grey body like a tail, which follows the 

 stomach, and is attached to it opposite to the 

 ovary. This body is round, very thin, and so 

 slender that it does not fill the tube in which 

 it is placed ; it is therefore difficult to imagine 

 that it descends to the base of the zoophyte 

 to unite with the rest." 



The above account, it will be perceived, 

 agrees very closely, as far as it goes, with 

 Milne Edwards's description of the anatomy 

 of the Alcyonidium ; but the last mentioned 

 naturalist has prosecuted the investigation of 

 these zoophytes still more minutely. 



In the Alcyons, properly so called, the 

 vascular system is very distinctly developed, 

 and in Alcyonium stellatum, more especially, M. 

 Milne Edwards was able to study it with faci- 

 lity. In this species he was enabled to detect 

 upon the parietes of the abdominal cavity of 

 the polype a variable number of minute aper- 

 tures irregularly dispersed, which are in im- 

 mediate communication with a system of ca- 

 pillary canals that traverses in all directions 

 the spongy portion of the polypary formed by 

 the external tunic of its component animals. 

 For in this species it is very easily seen that 

 while the internal tunic lines the abdominal 



cavity of the polype, the external layer, instead 

 of being confounded with the former, as in 



Fig. 34. 



Alcyonium stellatum. A portion of the polypary 

 divided longitudinally, showing the" ramifications of 

 the vascular system in the spongy substance sepa- 

 rating the abd'ommal cavity of the polypes ; on the 

 parietes of these cavities the mouths of many of 

 the vessels are seen. (After Milne Edwards.) 



the protractile portion of the animal, becomes 

 perfectly distinct from it at the point where 

 it begins to enter into the composition of the 

 polypary, at which its thickness becomes con- 

 siderably augmented, its texture spungoid, 

 and in its substance are deposited a number 

 of irregular crystals, composed of carbonate 

 of lime mixed with a little colouring matter. 

 In the tegumentary mass thus formed, the 

 vascular canals ramify, anastomosing freely 

 among themselves, so as to constitute a vas-> 

 cular network. These vessels are formed of 

 very attenuated membrane of a yellowish 

 colour, which is continuous with the internal 

 tunic of the polypes, and is perfectly distin- 

 guishable from the dense tissue with which it 

 is surrounded. The distribution of these 

 canals is best displayed by cutting a thin slice 

 of the mass of the Alcyon and removing the 

 crystals with which it is filled by immersion 

 in some dilute acid ; it is then seen that the 

 canals are most numerous and of the largest 

 size towards the extremities of the branches 

 of the polypary, and that they establish fre- 

 quent communications between the abdominal 

 cavities of the different polypes. This organi- 

 zation evidently establishes a very intimate 

 connection between the different polypes of 

 the Alcyon. The fluids with which their 

 bodies are filled must thus necessarily circulate 

 in the entire mass of the polypary, and if each 

 of the polypes has, on the one hand, an indi- 

 vidual sensibility, and a distinct digestive 

 cavity on the other, there is a vascular system 

 common to them all. 



The Alcyons, like the Alcyonide, are repro- 

 duced by ova, which are formed in membra- 

 nous ovaria of precisely similar construction, 

 and also by gemmae, which in the Alcyon are 



