178 MORSE, CLASSIFICATION OF MOLLUSCA 



duced to their primary elements, are sacs in one sense of 

 the word, though in one case a radiate sac, in another an 

 articulate sac, etc. Yet nowhere does this character pre- 

 dominate so universally, nor is it expressed so simply as in 

 the Mollusca; the leading idea as it were. It was shown 

 also that, essentially, the heart is on the outer bend of the 

 intestine, or between that and the sac wall, while the 

 principal nerve mass was on the inner bend of the intestine. 

 We would thus state their characters. 



SACCATA. 



(1) Animals of a varied form, without a radiate struc- 

 ture and without articulations. 



(2) Stomach and viscera enclosed by a fleshy sac, which 

 may be closed or open, at either one or both ends. 



(3) Principal nerve masses, consisting of ganglia, which 

 are adjacent to, or surround the (esophagus. 



(4) Intestine bending inward, or having an outward 

 flexure. 



(5) Heart on the outer bend of intestine. 



f Sac open at C Cephalopoda. 

 f Holozoic, or | anterior end. \ Gasteropoda, 

 typic. ■{ 



Saccata. ■{ 



Mouth opens ■ I Sac opens at C Lamellibraxchiata . 

 anteriorly. l^botn ends. £ 



Phytozoic, or f Sac open at C T rxICATA 

 hkmitypic. posterior end. ( 



Mouth opens ■{ 



I Sac closed. * Brachiopoda. 



b 



POLYZOA. 



We must now consider the relations of the Saccata to 

 the other branches of the Animal Kingdom. In the paper 

 of Professor Dana's, above referred to, he has used the terms 

 alphatypic, betatypic, and gammatypic, as a numbering 

 of the grades of types, whether of branches, classes, or or- 

 ders ; also, below gammatypic, we have degradational. 



The Radiates are regarded as degradational, and below 

 this, hemiphytoid, also, the terms used above, namely, 

 Holozoic, or true animal forms, and Phytozoic, or plant- 

 like forms. 



