564 



THE INVERTEBRATA 



Suborder DIOTOCARDIA 



Haliotis, the ormer (Figs. 380 C, 390 A), is a greatly flattened gastero- 

 pod which lives between tidemarks, as far north as the Channel 

 Islands, browsing on seaweed and eating all kinds of dead organic 

 material. It can move with considerable speed (5-6 yards a minute), 



Fig- 387. To illustrate origin of euthyneury in the Pulmonata, A, B, and the 

 Opisthobranchiata, C, D. After Naef. A, Chilina. The left parietal ganglion 

 (Lpa.g.) has moved forward owing to the shortening of its plural connective. 

 B, A pulmonate belonging to the Basommatophora. The corresponding con- 

 nective on the other side has shortened also, the visceral loop has become 

 untwisted and the nerve ganglia are concentrating. C, Actaeon, with short 

 spire and broad shell mouth, ctenidium and anus pointing to the right. 

 D, Bulla, showing slightly greater detorsion without spire, the shell mouth 

 opening to the right and anus pointing posteriorly: left parietal ganglion 

 drawn over right connective so that visceral loop is untwisted, an. anus; 

 au. auricle; ct. ctenidium; Lpa.g. left, r.pa.g. right parietal ganglion; ma.c. 

 mantle cavity; v. ventricle. 



but adheres very firmly to stones. The mantle cavity is very spacious 

 and contains two ctenidia, the left being rather the larger, each with two 

 rows of filaments. The mantle has a slit which runs in the roof of the 

 mantle cavity, its position being shown by a row of holes in the shell 

 which serve for the escape of the exhalant current. The anus opens 



