ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 433 



addition to these hairs, there is at the lower end of a pair of filaments 

 a small round spot where the epithelial cells carry stiff hairs. The 

 blood-vessel within the filament is divided into two halves by a 

 septum. 



The author directs attention to Bonnet's division of the gills of 

 Lamellibranchs into (1) filamentar, (2) lamellar, (3) folded, (4) 

 " coulisse " ; these four groups form a scale which increases in com- 

 plexity, but the divisions do not agree with any other division of 

 this class ; species belonging to the same family are found in the 

 most widely separated groups, and species of different families present 

 just the same arrangement of gills. This is illustrated by a table 

 and by various examples ; as also by a preceding detailed account of 

 the branchial arrangements of Modiolaria cUscors, Area glacialis, and 

 Astarte sulcata ; in this last form the outer lamella of the inner and 

 the inner lamella of the outer gill, contain venous blood, while the 

 other two lamellae contain arterial. 



B. INVERTEBRATA. 



MoUusca. 



Digestive Organs of the Dibranchiate Cephalopoda.* — In this 

 essay Dr. C. Livoro is principally occupied with histological details. 



The two lips are described as having very much the same structure, 

 and as being made up of epithelium, connective tissue, and muscular 

 fibres. On the free edge of the upper lip the first of these has not 

 pavement, but polyhedral cells, similar to those which are fonnd in 

 racemose glands. Where the lips unite the epithelial cells are 

 cylindrical in form, and this kind is found over all the lower lip, 

 save that on its inferior surface there is a horny cuticle, without any 

 definite structure. The muscular fibres are radial or circular. The 

 jaws are likewise inferior and superior, and are moved by powerful 

 muscles ; they consist of two solid convex and coucentrical layers 

 which unite in front to form the free cutting edge. The greater part 

 of the so-called buccal bulb is made up by the muscular masses which 

 move the jaws. The tongue is only free in its anterior portion, and 

 this is furnished with papillBS which are apparent to the naked eye ; 

 the constituent muscular portion is covered by a papillate mucous 

 membrane, the epithelial cells of which are cylindrical, and invested 

 by a cuticle which presents at certain points small horny papillae, 

 comparable to the denticles which are found on the radula. This 

 last is a solid cuticular plate, which is found on the surface of the 

 tongue, in its posterior region. The denticles on it are directed 

 backwards. The horny substance is homogeneous, and the ejiithelial 

 cells ai'e cylindrical. Behind the radula there are two lateral masses 

 of an irregularly pyramidal form, which touch one another in the 

 region of the pharynx, and then unite into a single mass. They 

 abound in connective tissue, in the midst of which a section reveals 

 muscles passing transversely, obliquely, or longitudinally. The inner 

 upper, and two-thirds of their outer surfaces are invested by a cylin- 

 * Journ. Anat. et Physiol. (Eobin), xvii. (1881) pp. 97-123 (2 pis.). 



