340 KOREN AND DANIELSSEN ON THE 



The head and the back of the animal are now distinct, and are 

 provided with fine ciHa and with much elongated tentacles, re- 

 sembling cilia. The eyes are more conical, and their lenses are 

 distinctly perceptible. The buccal aperture appears in the form 

 of a transverse cleft. The proboscis is perfectly developed. The 

 tongue appears in it with its armature such as Lebert and Loven 

 have described. The salivary glands are very voluminous, and 

 their excretory canals may be readily traced passing along the 

 sides of the oesophagus. The siphon is already much developed, 

 and provided with cilia (fig. 13 ^). The form of the foot is modi- 

 fied, being considerably elongated; in addition, two rounded 

 lobes have arisen in its upper part; its surface is ciliated all 

 over (11,12/). As regards its structure, the foot is composed of 

 a multitude of primitive muscular tubules — some cylindrical, 

 others varicose — running in all directions, without however 

 uniting into bundles. We have never been able to detect either 

 granules or cells in these tubes. 



At this period the nervous system has become very distinct. 

 We see that the two ganglia placed at the sides of the oesophagus 

 (cerebroid ganglia, 11 ^,12/?, 14/) are united by a commissure; from 

 each of these ganglia a very thick commissure passes (12^, 14 i) 

 to unite them to the pedal ganglia (12r, 14 A:), which are ovoid, 

 with their small extremities turned towards the cerebroid ganglia, 

 and furnish a great number of branches for the foot, (fig. 14 /.) 



We see besides, in the lobes of the foot, two smaller, also ovoid 

 ganglia (125, 14m) which send branches to the lobes. Two commis- 

 sures (14 w), unite them tothe pedal ganglia: the cerebroid ganglia 

 distribute a nervous twig to each eye and to each auditory or- 

 gan {I4g8ih). We have observed that one of the pedal ganglia 

 sends a nerve to the intestinal mass (fig. 14: p). 



The description given by Cuvier of the nervous system of this 

 mollusk* differs in many points from what our observations have 

 shown us. It is certain, that the nervous mass which Cuvier 

 has called the cerebrum is a pedal ganglion ; for we have seen, 

 in the adult animal, that the true cerebroid ganglion which sur- 

 rounds the oesophagus, and which, without doubt, escaped his 

 notice, is situated above this latter ganglion. 



♦ Memoires pour servir a IHistoire de VAnatomie des Mollusques. Paris, 

 817. 



