436 Messrs. Koren and Danielssen on the 



in an analogous manner to that of Buccinum undatum. It is 

 also plaecd on the back, a little towards the right. It contracts 

 strongly, giving forty to fifty pulsations in a minute. It is fur- 

 nished with primary muscular fibres, having the form of longi- 

 tudinal tubes a little enlarged above. We found neither granules 

 nor cells in these tubes. In this stage of development, the 

 branchial cavity not being sufficiently deep to contain the whole 

 heart, a considerable portion issues from it and passes the mar- 

 gin of the mantle. Subsequently, when the mantle becomes 

 elongated and covers the back of the animal, its margin is 

 directed more outwards, and removes from the body in such a 

 way that the cavity, becoming deeper and more ample, encloses 

 the entire heart. We have not been able to follow the rest of 

 the circulatory system. 



It is not until after these organs are formed that we observe 

 the buccal orifice, with the pharynx and oesophagus, at the point 

 where the rotatory organs meet on the back. The proboscis in this 

 stage is exceedingly short, and its walls are pretty thick, so that 

 the oesophagus is detected with difficulty. It is a cylindrical 

 canal, which runs directly to the stomach. From the stomach, 

 which is small and oval, issues a long and slender intestinal 

 canal, which passes to the right, then returns to the opposite 

 side, describing a curve, and at length terminates a little towards 

 the right by an anus projecting into the branchial cavity. The 

 oesophagus and also the stomach and intestines are clothed with 

 cilia on their inner surface. 



The salivary glands have also become enlarged ; their cells 

 are more approximated, and form long rows. In their broadest 

 part a multitude of yellow pigment-grains are seen. In their 

 more slender portion, which is turned towards the oesophagus, 

 the excretory duct of the gland makes its appearance, and be- 

 comes elongated to meet the oesophagus. The salivary glands 

 in the adult animal form a coherent mass, but their double 

 excretory duct clearly indicates that this was formerly divided. 

 On each side of the oesophagus we perceive the two cerebral 

 ganglia, which are here distinguished from the common mass 

 by their yellow colour. These ganglia are united to each other 

 by a commissure, and give origin to two other commissures, 

 which unite them with the two pedal ganglia. We have found 

 it impossible to trace the nervous system any further, all the 

 parts of the body having rapidly become opake. We suppose, 

 however, that it agrees for the most part with that of Buccinum. 

 It is also about the period at which the nervous system appears, 

 that we distinguish the first traces of the branchiae, the siphon, 

 and the retractor muscles of the foot. The branchise originate 

 from the margin of the mantle, where they form a hollow cylin- 



