^^ 38, 39. THE POLYPI. 47 



DIGESTIVE CAVITY OF BRYOZOA. 



§ 38. 



The very complicated digestive canal of the Bryozoa floats freely in the 

 spacious cavity of their body. It is composed of an oesophagus which, at 

 its lower extremity, dilates into around or oval muscular crop;*^' upon this 

 immediately succeeds a cojcal stomach, from the upper portion of which a 

 small intestine arises and passes upwards in front. This, after a course of 

 variable length, ends by a constriction in a short but large rectum, which 

 opens in the vicinity of the mouth, at the external side of the base of the 

 tentacles.® The digestive canal here, therefore, is not in communication 

 with the cavity of the body. Its whole inner surface is lined with very 

 active, ciliated epithelium, which keeps its contents in motion, and especially 

 the fseces of the rectum. The sides of the stomach are often colored brown, 

 yellow or green, from the presence of hepatic cells.t 



CHAPTEKS VI. AND VII. 



CIRCULATORY AND RESPIRATORY SYSTEMS. 



§ 39. 



A vascular system has yet been found only with a few Polyps ; but there 

 it is so apparent that its presence in others may be inferred. The blood- 

 vessels exist upon both the sides of the body and of the stomach, and are 

 in part longitudinal, in part circular, ending in a capillary net-work. They 

 are not simple canals excavated in the parenchyma, but have proper walls, 

 and circulate a liquid containing a great number of white (blood) globules.*'* 



juice of the Anthozoa must have a very great 1 Milne Edwards has perceived a vascular net- 

 digestive power, since the Jciwia eat hard-shelled work of this kind in the sides of the body, witli 

 Crustacea, and even the soft Hydrae quickly dis- Alcyonidium elei^ans, and Alcynnium palma- 

 solve the larvae of Nats and Chironomus. But turn and stellatum (Ann. d. Sc. Nat. IV. p. 

 the indigestible parts ot these animals, such as ejii- 338). Quite recently, IVill has described the vas- 

 dermis, bristles, hooks and jaws, are afterwards c-aVATsysltixa oi Alcyonium palmatum {VToriep''s 

 ejected by the mouth. neue Notizen, 1843, No. 599, p. 68). According to 



1 In Boinerbankia {Farre^ Phil. Trans. 1837, him, white vessels may be perceived, even with the 

 p. 392, PI. XX. fig. 5 ; PI. XXI. fig. 7) this crop naked eye, upon the longitudinal furrows of this 

 is composed of pyramidal corpuscles, with the animal. These enter the lol)ules on the border of 

 apices pointing inward, so as to act like teeth. I the body, and there form a dense net-work, from 

 have observed a very similar structure in Alcyo- which a branch is sent to each arm, and this last 

 ne.lla sta^norum. gives off laterally a twig to each tactile lobule. The 



2 In Rowe.rbankia and Vesicularia the small principal trunk of the longitudinal vessels con- 

 intestine is very long {Farre. loc. cit. PI. XX. and tinues upon the sides of the stomach to the base of 

 XXII). I have observed it very short with Cris- the tentacles. At the point where the bodies of 

 tatella mirabilis.* the Polyps continue with the corallum, there are 



* [§ 38, note 2.] According to Allman (Report wide at first, passes along the side of the cardiac 



Brit. Assoc. 1850, p. 310), the oesojjhagus succeeds cavity and oesophagus, and rapidly decreases in 



the stomach without the intervention of any dis- diameter, until it terminates in a distinct anu3 just 



tinct crop with all the fresh-water Bryozoa. The below the mouth. — Ed. 



stomach is large and thick-walled, and may be t [ Note at end of § 33.] Sec in this connection 



divided into a cardiac and a pyloric portion. The my note under § 13, note 2. — Ed. 

 pylorus 13 distinctly valvular, and the intestine, 



