72 H. HEATH lind M. H. SPAULDING, 



cases almost completely filling the cavity of the casque. Whether this 

 chamber communicates with the pericardial cavity is uncertain; on 

 the other hand the outer opening, situated ventrally on the right side 

 is surrounded by a sphincter muscle that renders it a conspicuous 

 feature. 



The Nervous System and Sense Organs. 



The central nervous system of Corolla conforms to the highly 

 centralized type characteristic of gymnosoraatous pteropods in general. 

 Cerebral, pleural, pedal and visceral ganglia, situated about the middle 

 of the oesophagus (Figs. 3—5, 7), are so closely appressed that the 

 commissures connecting them are usually invisible except in sections. 

 The cerebral ganglia (c), located on each side of the oesophagus, are 

 connected dorsally by a heavy commissure, practically devoid of ganglion 

 cells and entirely free from branches. From their anterior borders 

 two large nerves arise and pass into the tissue of the proboscis. The 

 inner larger cord (Figs. 3, 4 c^) supplies the lips and oesophagus 

 anterior to the brain. In favorable surface views its finer branches 

 appear to form a delicate plexus ensheathing the oesophagus and con- 

 necting with ganglion cells that are irregularly disposed in the sui)er- 

 ficial portions of the gullet. This plexus will be more fully described 1 

 in connection with the buccal nerves. The outer more slender • 

 cerebral nerve (c^ divides very soon after leaving the brain, 'i'he 

 inner limb passes directly to the lips where it breaks up into numerous 

 branches. The outer nerve, after giving rise to a delicate twig passing 

 up to the tentacle, courses forward and innervates a part of the pro- 

 boscis proper and a portion of the lips. 



From the inner surface of the cerebral ganglia the buccal com- 

 missure arises and extending inward becomes attached to the closely 

 fused buccal ganglia (Figs. 4, 5). From the anterior surface of each 

 buccal ganglion a nerve (6) is developed and after extending outward 

 to the lateral borders of the oesophagus courses along the latter sup- 

 plying it with delicate branches at least as far forward as the level 

 of the tentacles. Posteriorly from each buccal ganglion a nerve (6^) 

 extends and rapidly divides into numerous branches extending over 

 the oesophagus back of the central nervous system and a few fibres 

 may be traced to the stomach. In specimens that have been partially 

 cleared in glycerine it is possible by means of fairly high magnification 

 in strong sunlight to see that the branches of both the anterior and 

 posterior buccal nerves from extensive anastomoses completely en- 



