156 



ANIMAL PHYSIOLOGY. 



[LESSON 44. 



FIG. 253. 



warty in many species, but is always found to be smooth and lubri- 

 cous on its internal surface. 



692. This tunic is lined by another, a muscular coat, of great 

 beauty as regards the arrangement of its fibres (Fig. 252) ; in this 

 animal (Cynthia pupa) the muscles consist of long diverging fasci- 

 culi, which originate from around the two orifices of the sac (a, b), 



and extend round the entire body 

 of the animal. These fasciculi are 

 attached to various points of the 

 exterior tunic, but most intimately 

 around the respiratory (a) orifice, 

 and the vent (5), which are also 

 provided with distinct and strong 

 sphincter muscles (c, d), passing in 

 a circular manner around them. 



693. The organs of nutrition 

 in these animals are peculiar in 

 their arrangement; thus, we find 

 the mouth proper, or entrance into 

 the nutrimental canal, placed at 

 the bottom of the sac (g, Fig. 253) ; 

 the food arrives at the mouth di- 

 rectly from the external respira- 

 tory aperture (a), being directed 

 to it by the spiral respiratory cur- 

 rent, caused by the vibratile cilia 



lining the respiratory sac. The 

 organs, Cynthia pupa. m()uth leadg ^ ^ oesophagug Q 



tolerable length, and ends in a well-formed, muscular cavity (&), 

 sometimes folded longitudinally, and perforated at the pyloric ex- 

 tremity by the wide ducts of the biliary follicles (/,/). 



694. Neither teeth, jaws, nor salivary glands, are found in con- 

 nection with this very simple alimentary canal, but the liver is al- 

 ways found, under some follicular form, opening into the cavity of 

 the stomach, as in other mollusca. The intestine forms a distinct 

 curvature, in an upward direction, behind the respiratory sac ; it 

 terminates opposite to the vent (6), and ends with a margin of vibra- 

 tile cilia, to compel, by their action, the discharge of effete particles 

 of matter. 



695. The ovaria (k) and the oviducts (m) lie on the inner side 

 of the intestine, the latter terminating by a margin of vibratile cilia, 



