32 



KR. BONNEVIE. 



[REP. OF THE "MICHAEL SARS" NORTH 



Jf 



w 



JF 



Fig. 27. Diagrams of the digestive tracts of Limacinidae (1 — 3) and Cavoliniidae (II — IV). 1. Peraclis diversa : 2. Limacina 

 helicoides: 3. Limacina balea; II. Clio falcata; III. Clio cuspidaia: IV. Clio pyramidata. All figures are drawn in dorsal 

 view, and parts of the intestine lying on the ventral side of the body are drawn in dotted lines. The unpaired tooth of the 



stomach is represented by a small triangle. 



textfig. 27 3 — IV). In Limacina the unpaired tooth of 

 the stomach is found on the dorsal side; the intestine 

 leaves the stomach in a direction towards the right and 

 makes a loop in which the rectum assumes a dorsal 

 position; the anus is found on the right side of the body 

 (see textfig. 27, 3). In typical Cavoliniidae, on the con- 

 trary, the unpaired tooth is found ventrally within the 

 stomach, the intestine first turns towards the left and the 

 rectum passes forwards ventrally and on the left side of 

 the body, where the anus is found (textfig. 27, IV). 



This fundamental difference between the two groups 

 night well be explained according to Boas' hypothesis by 

 a rotation ("of 180") of the whole digestive tract, and 



considering only the typical representatives of both groups, 

 like Limacina balea and Clio pyramidata this would, in 

 fact, seem the only possible explanation. And yet an 

 investigation of the more archaic forms proves that the 

 relations of the digestive tract in typical species of Lima- 

 cina and Cavoliniidae are not to be compared directly 

 with each other, but that they ought to be considered as 

 the corresponding final results of two diverging lines of 

 development both taking their origin in a state like that 

 found in the genus Peraclis. 



The digestive tract of Peraclis (textfig. 27, 1) shows 

 all the essential characteristics of the Limacinidae, regard- 

 ing the position of the unpaired tooth and the anus, 



