116 HALF-AN-HOUR 



Willow Branch, transverse section. — I simply remark on this 

 section that Raphides in great quantities will be found in the bark 

 of Willow as Crystal prisms and Sphaeraphides, also Crystal- 

 dust. Query — Are not these larger Crystals in course of forma- 

 tion ? 



Sclerogen from Pear. — I recommend the following plan for 

 preparing this object : — Cut sections and dry between slips of 

 glass tied together ; then mount as you would a section of bone, 

 of plum- or cherry-stone, of cocoa-nut shell, or of vegetable ivory, 

 in hard balsam. This will just make the object sufficiently trans- 

 parent for comfortable examination, but will not obscure the cana- 

 liculi by running into them. The result will be found very striking 

 and satisfactory. 



Palate of Helix aspersa, and 



Palate of Periwinkle (Littoria littorina) form a choice pair 

 that will be best considered together, forming, as they do, so 

 striking and interesting a contrast. The one (comparatively) so 

 short and many-toothed ; the other is very long, and having, in 

 comparison, so few teeth. Better types could not have been 

 selected. And they have the further advantage, that both the 

 animals whence they are taken are readily to be procured by other 

 members for their own study and comparison. For whatever may 

 be said to the contrary, it is the fact that the common objects 

 wherewith we are surrounded are those whose structure it is most 

 important we should be conversant with, as they are those which 

 are almost invariably selected for typical illustration by the 

 Masters in Science. 



Palates should be mounted in cells, and not pressed flat. In 

 the mouth of the snail two muscles will be seen : one of these 

 draws the tongue up, the other is employed in drawing it down. 

 The forward part is drawn alternately up and down, the leaf being 

 held firmly by a large, strong tooth, represented by the labrum in 

 insects. The forward portion of the dentigerous cartilage rasps 

 off pieces of the leaf, which are then swallowed. It is very 

 interesting to notice the surprising rapidity with which this is 

 effected. The tongue is somewhat spatula-shaped, both in front 

 and behind;, the intermediate and larger portion in length being 

 much bent down at the sides. The hinder expansion represents 

 the lower portion of the walls of the pharynx. See Plate XIII. 



In the Periwinkle things are very different. Here the front 

 (acting) teeth are seated in a narrow band along the centre of a 

 delicate, elongated cartilage, the remainder extending, in coil upon 

 coil, some distance behind the front of the head. 



