38 BRITISH MOLLUSKS. 



and the Brazils, Vitrina is represented by quite a different type, 

 Simulopsis, in which the shell is ribbed and more inflated; and, as it 

 has a less vitrified polish, it is probably not enveloped to the same 

 extent by the reflected lobe of the mantle. 



What, then, is there in the structure of our solitary example of 

 Vitrina which renders it of so much interest ? The animal, it will 

 be seen, possesses the shield and respiratory orifice of the slug 

 along with the spirally whoiied shell of the snail. The mantle, 

 secreting a light glassy-horny shell of three rapidly enlarging whorls, 

 is produced in front of the aperture in a thickened manner, extend- 

 ing conspicuously towards the head ; and behind, on the right side, 

 posterior to the respiratory orifice, it is lobed, so as entirely to cover 

 the shell, and, by its action, keep the shell bright and shining. The 

 action of this retractile lobe, when the animal is in motion, tends to 

 give a highly vitrified pobsh to the shell ; and it has been observed 

 to move even when the animal is at rest. The shell of Vitrina, 

 not only of the British but of all the numerous foreign species, is 

 composed of the simplest glassy or horny membranaceous substance, 

 more or less soft and yielding to the touch in the living specimen. 

 After death, when the animal dries up, the shell, in the absence of 

 the living body and its mucous secretions, becomes brittle. 



For information of the habits of the genus, it is necessary to refer 

 to the foreign as well as to the British species. Mr. Cuming, who 

 collected Vitrincs in abundance in the Philippine Islands, was parti- 

 cularly struck with their activity. He relates, that on placing them 

 on the palm of his hand they kept jumping up, with sudden leaps, 

 by the muscular action of the foot; and Mr. Benson mentions this 

 habit in reference to an Indian species observed to have the power 

 of springing several inches from the ground. ISTilsson, the Swedish 

 naturalist, describes some interesting experiments on incubation. 

 Specimens, as related on his authority by Gray, caught at the end 

 of January were kept in a bell glass, and on the 19th of February 

 eggs were observed to have been deposited on putrescent leaves. 

 The eggs were hi little tufts of eight or nine, subpellucid, marked 

 with a central opake white spot. In the beginning of March, the 

 opake spot was not increased in size, but showed signs of slow 

 movement, and on the 21st or 22nd of the month, the animals were 

 excluded. When observed with the microscope, the animal was 

 thought to be boring its way through the egg-shell, forming a hole 

 out of which first the head and then the foot were protruded ; when 

 first hatched, both animal and shell were fully formed, the tentacles 

 being retracted into the body. 



