Miscellaneous. 383 



idea of the unity of the functious of reproduction in plants — an idea, 

 however, which he ascribes to M. Sachs, who put it forward in his 

 * Lehrbuch der .Botanik,' published at Leipzig in 1868. Whatever 

 value we may attach to his conclusions, this memoir of M. Millardet's 

 possesses great interest. It is only to be regretted that the plates, 

 which the author intends publishing hereafter in a scientific perio- 

 dical, do not accompany the memoir itself. — Notice of a ivork published 

 at Strasbourg in 1869 ; from Bibl. Univ. March 15, 1870, Bull. Set. 

 p. 275. 



Morphological Researches on the Mollusca. (First Memoir : Gastero- 

 pods.) By M. Lacaze-Duthiers. 



One of the most difficult types of the Mollusca to reduce to a 

 theoretical plan is undoubtedly that of the Gasteropods. I propose 

 to show that, by taking the relations of the organs and of the ner- 

 vous system, it is always possible to refer the various forms to a 

 single plan. 



Let us reduce the body of the Gasteropod, for the sake of simpli- 

 city, to four parts — the head, the foot, the visceral mass, and the 

 mantle. If we iinroll the body of a species with a turbinated shell, 

 we shall have beneath the head and behind and below the foot a 

 reversed cone containing the viscera*. 



The relations of these parts are essentially variable. Thus the 

 head is often separated from the visceral mass by a true neck. As 

 to the mantle, its morphology is difficult. 



The study of the embryo of Am-i/lus enables us with ease to re- 

 cognize this organ from its origin. In fact, upon the embryonic 

 sphere, the head first betrays itself by the formation of the mouth. 

 Soon two disks, bounded by a circular cushion, show themselves, 

 the one near, the other opposite to the mouth : the former is the 

 foot, the latter the mantle. At this moment the Ancylus represents 

 the ideal being with the four principal jmrts. 



Starting from this state, we may vary the forms and explain the 

 modifications of the Gasteropod-type. But, in the first place, to have 

 an exact idea of the mantle, let us suppose the embryonal disk from 

 which it is derived eminently elastic and extensible ; let us assume, 

 further, a traction exerted upon its centre and directed backwards, 

 and we shall obtain a reversed cone, of which the apex will be the 

 point of application of the force of traction, and the base the part of 

 the body bounded by the circular cushion of the primitive disk. 

 The intestines will penetrate by traction into the cone thus formed ; 

 but the foot and the head will remain without. These four parts 

 will be deformed, but their relations will remain constant. 



It is then easy to account for some forms which are very different 

 in appearance. For example, in the Li maces the foot increases 



* To understand this, the animal is supposed to have the head above, 

 the foot in front, and the apex of the spire and the mantle behind and 

 below. 



