^41. 



THE POLYPI. 



49 



while the tentacles, in the cavities of which are regular currents, serve as 

 external organs of respiration, similar to branchiae. 



But, if we regard the whole as a true circulation, the contained liquid 

 with its corpuscles will be analogous to blood. But this view is opposed 

 by the fact that, with Alcyoiiimn, with Actinia, and perhaps many other 

 Polyps, there is a true vascular sanguineous system. <^> 



We ought, therefore, to compare the liquid in question to chyle, which 

 passes from the stomach to the general cavity of the body, in the Bryozoa 

 by exosmose, but in the Anthozoa by the orifices of the stomach.® 



The opinion that these currents form a vascular system, moreover, is not 

 reconcilable with the fact that the Anthozoa can at will empty the contents 

 of their stomach into it, or in the same way shut ofi" from it the water. 



We are obliged, then, to regard all these cavities as constituting a 

 vascular aqueous system, performing a respiratory function, by which, 

 in the Anthozoa, all the internal parts are constantly bathed with fresh 

 water. This renewal of water is effected by its alternate ingress and 

 egress through the stomach,® during which chyle-corpuscles could easily, 

 by being mixed with water, be carried into this aqueous system. 



With the Bryozoa, where this system is, without doubt, equally one of 

 respiration, we shall have to seek for the openings by which this renewal 

 of water takes place. These are situated near the anus, and place the 

 cavity of the body in direct communication with the external water.*'*' 



1 See §. 39, note 1. 



2 Ehrenberg and Lov^n regard the canals of 

 the corallum of Campanularia and Scrtularia as 

 direct prolongations of the stomach, and designate 

 them as intestinal tubes, and their contents as 

 chyme. 



3 This alternate ingestion and egestion of water 

 has been positively observed by Lister, Loven and 

 Van Beneden, in Sertularia and Tubu/aria. 



i By an opening of this kind, Meyen (Isis 1828, 

 p. 1228) saw escape the eggs of Alcyonella sta^- 

 nalis, which were free in the cavity of the body. 

 Fare Beneden (Ann. d. So. Nat. XIV. 1840, p. 

 222) declares that he has observed at the base of 

 the tentiiclos of Alcyonella a series of orifices, 



* [ End of § 41.] In this connection should be 

 mentioned branchia-like organs, described by Dana 

 (loc. cit. p. 42) with the Zoantliina. A pair of them 

 is attached to each of the larger lamellag. He 

 remarks, " The structure of these organs is such 

 that we can hardly doubt their branchial nature ; 

 yet no circulating fluid was detected within them." 

 I find no other mention of these parts, except by 

 Lesueur (Jour. Acad. Nat. Sc. Pliilad. 1. 183-185, 

 PI. VIII. fig. 1, 5, 9), who regarded them as of an 

 hepatic nature. — Ed. 



t I § 41, note 4.] The ti-ue nature and relations 

 of the respiratory and circulatory systems of the 

 Bryozoa are yet imperfectly understood. There 

 can be but little doubt that water is by some means 

 introduced into the general cavity of the body, and 

 there mingles with the nutritive fluid, which trans- 



wliich may be called aquiferous mouths, for by 

 them the water enters the cavity of the body. 

 This is perhaps the case with Actinia, also; for 

 Rapp (Ueb. die Polypen u. die .\ktinien, loc. cit. 

 p. 47) has here found numerous small orifices 

 scattered over the whole surface of the body, and 

 through which are emitted jets of water when the 

 animal is squeezed, thus showing that they belong 

 to an aquiferous system. It is quite improbable 

 that the hollow tentacles of Actinia are open by 

 an orifice at then- apex for the circulation of water, 

 as many naturalists have supposed. Quatre- 

 fages (Ann. d. Sc. Nat. XVIII. p. 96) is quite 

 opposed to this opinion. See also above § 36, 

 note l.t 



udes through the walls of the alimentary canal. 

 But the apertures for the introduction of this water 

 have not yet been clearly seen. It is true that 

 Van Beneden thinks he has found " Bouches aqui- 

 f^res," as above mentioned, but their existence 

 there has not been fully verified, and is even 

 denied by Allman. At present, therefore, it cannot 

 be said that the Bryozoa have a true aquiferous 

 system, like the Anthozoa. The perigastric fluid 

 is, separated from the water, most probably the 

 elaborated product of digestion, and the corpuscles 

 therein contained chyle-corpuscles. Allman's 

 view, therefore (Report Brit. Assoc. 1850, p. 319), 

 appears the most correct : " The perigastric circu- 

 lation, therefore, unites in itself the triple function 

 of a chyliferous, sanguiniferous and respiratory 

 system." — Ed. 



