363 Messrs. Koreu and Danielssen on the 



nates in a ganglion (<?). From the same part arises a more deli- 

 cate branch, which runs to the heart {q). From the ganglion (e) 

 issue two branches (r r), which pass to the intestines. When 

 the animal is perfectly developed, the ganglia unite, and form a 

 single cerebral mass. 



The shell, which, at the commencement of the formation of 

 the embryo, was very delicate and membranous, and which was 

 at first of an oval or reniform shape, subsequently acquires the 

 form of a Nautilus, but becomes more oblong by degrees. The 

 calcareous matters then begin to be deposited in great quantity, 

 so that a layer of transverse and longitudinal striae is distinctly 

 formed, causing the shell to be less transparent than before. 

 However, the internal organs may still be seen. Both the heart 

 and the vesicle have become divided into two chambers, of which 

 the superior is the smaller. We also observe a strong muscle 

 which starts from the inner face of the shell, and passes to the 

 foot (PL XVI. fig. 3 r). Finally, we observe a small dark body, 

 consisting of cells containing a yellow pigment ; almost imme- 

 diately afterwards, a similar body makes its appearance quite 

 close to this, and this is followed by a third. These three bodies 

 become blended together, and form the liver, which is somewhat 

 oblong (fig. 3 u). On the inner wall of the mantle we perceive 

 a series of folds, in which a mass of mucous glands is situated 

 (mucous laminae). In proportion as the young animals grow, 

 still more calcareous matter appears in the shell, the mantle be- 

 comes thicker, and it is almost impossible then to distinguish 

 the internal organs. The two rotatory organs have coiiipletely 

 disappeared, and behind the tentacles v/e see a raised line, which 

 shows the position in which they were situated. Tlie shell has 

 acquired a yellowish colour, and become hard, brittle, and only 

 semitransparent. When the young animals abandon their cap- 

 sules, they begin to creep, with the tentacles, the foot, and the 

 siphon extended. They differ from the adult animal only in the 

 shell, which has not, as yet, more than one or two turns of the 

 spire. At the end of five months, the shell is completely de- 

 veloped, and if we examine a young animal in this stage, we do 

 not yet find any traces of the organs of generation, and the 

 grouped eggs still fill the hinder part of the shell. 



This is the way in which the development of Buccinum unda- 

 ium usually takes place. Thus only by an assemblage of well- 

 organized eggs coming together to form the embryo, can it, in 

 its ulterior growth, attain such a perfection as to be in a condi- 

 tion to continue an independent existence. But, by the side of 

 this extraordinary development, comes a series of phfenomena, 

 which, on the one hand, follow the ordinary law of the develop- 

 ment of animals of the lower classes, and consequently diflfer 



