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MANUAL OF ZOOLOGY. 



of the mantle, and has its walls perforated by numerous aper- 

 tures. This is known variously as the "pharynx," the "respi- 

 ratory sac," or the "branchial sac." (It must be remembered 

 that the aperture here spoken of as the mouth can only be 

 looked upon in this light provided that the respiratory sac is 

 looked upon as the pharynx. By Professor AUman, whose 

 definition is given at the head of this chapter, this view is not 

 accepted, and consequently the internal or inferior opening of 

 the respiratory sac is regarded as the true mouth.) Inferiorly 

 the respiratory sac leads by a second aperture into an ceso- 

 phagus, which opens into a capacious stomach. From the 



Fig. 103. — Morphology of Tunicata. i. Diagramof a Tunicary (after Allman): <7 Ora 

 aperture ; b Atrial aperture ; c Pharyngeal or branchial sac, with its rows of ciliated 

 apertures ; d Alimentary canal, with its hsemal flexure ; e Anus ; f Atrium ; g Ner- 

 vous ganglion. 2, Cynihitt papulosa, a simple Ascidian (after WoodwardJ. 



stomach an intestine is continued, generally with few flexures, 

 to the anal aperture, which does not communicate directly 

 with the exterior, but opens into the bottom of a second cham- 

 ber, which is called the "cloaca:" (fig. 103, i,/). Superiorly 

 the cloaca communicates with the external medium, by means 

 of the second aperture in the test. The first bend of the 

 intestine is such that, if continued, it would bring the anus on 

 the opposite side of the mouth to that on which the nervous 

 ganglion is situated. The intestine, therefore, is said to have 

 a "haemal flexure;" whereas the flexure in the case of the 

 Polyzoa is " neural." The intestine, however, in the Tunicata 

 does not preserve this primary hsemal flexure, but is again 

 bent to the neural side of the body, the nervous ganglion coming 



