Misce Uaneous. Ill 



whoroupon a cystic membrane is differentiatcfl. As to what ha|jpcn8 

 aftorwards and in the interior I um sorry to say that I am unable a8 

 yet to give any account. Novertliclcss it was still possible to see 

 that the cavities of the intestines disappear, a])pareiitly owing to 

 continued niultii)lication of cells, so that finally the entire contents 

 of the cyst are composed of similar cells. 1 am inclined to believe 

 that each of these cells represents a younrj animal, which, after 

 being set free, roves about by aid of its cilia like one of the Ciliata, 

 and by further division develops into the adult form ; for I observed 

 in the same salt-water small unicellular organisms, ciliated on the 

 ventral surface only, yet bearing a few cirri in front. These are 

 possibly the young forms (larva?). — Zooloijischer Anztiijer, xiv. 

 Jahrg., no. 3G7 (13th July, 18U1), pp. 23U-233. 



On the Growth of the Shell in Helix aspersa. 



]3y M. MoYNlEU DE YlLLEPOIX. 



We know that the growth of the shell in pulmonate Gastropods 

 takes place by the formation, at the edge of the test, of a soft and 

 diaphanous zone, which speedily hardens. I have specially studied 

 this formation in Helix aspersa, L. 



The epidermis which gives rise to it is particularly interesting 

 owing to the hyaline spherical globules, 10 yu to 12 yu in diameter, 

 which cover its outer surface. Their nature is organic ; they persist 

 on the oldest shells, and I have reasons for thinking that it is to 

 similar formations that we must attribute the markings which are 

 to be found on almost all the shells of the genus Helix. 



In animals in course of growth, the thickened border of the mantle 

 is always applied against the peristome, and the free edge of the 

 epidermis, folded inwards, buries itself, but without any connexion 

 with the tissues, in a very narrow cleft which runs round the whole 

 circumference of the collar. Immediately behind this cleft, we 

 observe beneath the epidermis a white zone bounding the mantle in 

 its entire breadth. 



The deposition of calcareous matter takes place on the internal 

 face of the epidermis, at some distance from its margin. The origin 

 of these products can be understood by examining sagittal sections 

 of the collar and mantle. 



The white zone, or bandelet, is a gland composed of flask-shaped 

 cells, with very long necks, and granular contents, which bury 

 themselves deeply in the subjacent tissue. The action of acetic acid 

 and oxalate of ammonia discloses the presence of calcareous matter 

 in these cells. 



Behind this bandelet the mantle is clothed with a columnar epi- 

 thelium, containing pigment or colourless granulations. 



Immediately in front of the bandelet the epithelium invaginates 

 to form the groove in w-hich is lodged the free extremity of the 

 epidermis. The bottom of the groove is occupied by an irregular 

 plexus of cells, which, in a sagittal section, present the appearance 

 of epithelial cells cut obliquely and extending to a greater or less 

 distance into the connective tissue. These cells contain transparent 

 spherules, presenting all the characters of the globules of the 

 epidermis. 



