ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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plates which appear, on each side, below the eye-tentacle, and grow in 
deeper and deeper until they finally come into contact with the cerebral 
ganglion of one side or the other. The lumen of the tube subsequently 
closes and loses its connection with the external epithelium, till at last 
it is transformed into a roundish mass which becomes completely fused 
with the corresponding cerebral ganglion ; the boundaries of the original 
can, however, be subsequently made out as the small constituent elements 
take a much deeper stain than those of the cerebral ganglia. The 
author agrees with the Doctors Sarasin, the original discoverers of these 
tubes, in regarding them as corresponding to the cephalic pits and 
similar organs of various worms. 
Growth of Shell of Helix aspersa.* — M. Moynier de Villepoix has 
investigated the growth of the shell of this snail. The epidermis with 
which it begins is peculiarly interesting on account of the presence of 
hyaline spherical globules, 10-12 ^in diameter, which cover its outer sur- 
face. They are organic in nature, and persist in the oldest shells. Calca- 
reous matter is deposited on the inner surface of the epidermis at some 
distance from its edge. There is a white zone which is a gland formed of 
lageniform cells, with very elongated necks and granular contents ; this 
is shown to contain calcareous matter. Behind this zone the mouth is 
covered by a cylindrical epithelium which contains pigment or colourless 
granules. In front of the zone the epithelium is invaginated to form 
the groove in which the free extremity of the epidermis is lodged. 
The bottom of this groove is occupied by an irregular plexus of cells, 
which appear to be epithelial ; they contain transparent spherules, 
which present all the characters of the globules of the epidermis. This 
tissue forms a series of pockets in the connective tissue ; the spherules 
grow at the expense of the protoplasm of the cells, which at last contains 
nothing but them. When set free the spherules collect on the fine 
organic membrane which is secreted by the epithelium. 
The calcareous glands of the collar do not take any part in the 
formation of the shell, which is formed solely by (1) the pallial groove, 
in which are found the epidermis and the glandular pouches which 
produce the globules and which are now described for the first time ; 
(2) the pallial band or gland which secretes the calcareous matter; 
(3) the pallial epithelium behind the gland which furnishes the 
pigment for the shell, and completes its calcification by the deposit of 
organo-calcareous layers, homologous with the nacreous layer of Lamelli- 
branchs. When the animal has attained its definite size the band and 
the globule-glands completely disappear. The epithelium of the mantle 
and of the pulmonary sac alone remains active to serve in the internal 
thickening of the shell and not to repair its losses. The secretory 
activity of the pallial epithelium is so great that the author was able, 
for a period of two months, to see animals, deprived of food, reproduce 
every day the organo-calcareous membrane which he removed every 
morning. 
Habits of a Murex.f — Dr. Ph. Francis writes that he has observed 
a species of Murex (“ 31. fortispinna at Noumea, in which one of the 
* Comptes Rendus, cxiii. (1891) pp. 317-9. 
t Arch. Zool. Exper. et Gen., ix. (1891) pp. 240-2 (1 fig.). 
