114 



Dr. F. M. Balfour and Mr. W. N. Parker. [Dec. 8, 



In the developmental section devoted to the eye the main subject 

 dealt with is the nature of the mesoblastic structures entering the 

 cavity of the optic cup, through the choroid slit. It is shown that a 

 large non-vascular mesoblastic process first enters the optic cup, and 

 that together with the folded edge of the choroid slit it forms a rudi- 

 mentary and provisional processus falciformis. At a later period an 

 artery, bound up in the same sheath as the optic nerve, enters the 

 optic cup, and the vascular membrane found in the adult then becomes 

 developed. 



The Suctorial Dish. 



The structure of a peculiar larval suctorial organ, placed at the 

 end of the snout, is described, and the organ is shown to be formed 

 of papillae composed of elongated epidermic cells, which are probably 

 glandular (modified mucous cells), and pour out a viscid secretion. 



Muscular System. 



The lateral muscles of Lepidosteus are shown to differ from those 

 of other fishes, except the Cyclostomata, in not being divided into 

 a dorso-lateral and ventro-lateral group, on each side of the body. 



Vertebral Column and Bibs. 



This section of the paper commences with a description of the ver- 

 tebral column and ribs of the adult. In this part special attention is 

 called to a series of cartilaginous elements, placed immediately below 

 the ligamentum longitudinale superius, which appear to have escaped the 

 notice of the anatomists who have previously worked at Lepidosteus. 

 These elements are shown to be intervertebrally situated. 



With reference to the ribs the authors point out that for the greater 

 part of their length they course along the bases of the intermuscular 

 septa, immediately external to the peritoneal membrane, but that their 

 free extremities bend outwards and penetrate between the muscles 

 along the intermuscular septa till they nearly reach the skin. 



In the embryological part of this section a detailed account is given 

 of the development of the vertebral column, of which the following is 

 a summary : — 



There is early formed round the notochord a mesoblastic investment 

 which is produced into two dorsal and two ventral ridges, the former 

 uniting above the spinal cord. Around the cuticular sheath of the 

 notochord, an elastic membrane, the membrana elastica externa, is 

 next developed. The neural ridges become enlarged at each inter- 

 muscular septum, and these enlargements soon become converted into 

 cartilage, thus forming a series of neural processes, riding on the 

 membrana elastica externa, and extending about two-thirds of the 



