337 



between these two extremes. The most common among existing 

 species is the Amphistegina gibbosa, which is very extensively dif- 

 fused through the tropical ocean, and which, though generally of 

 small size, acquires in the Philippine region dimensions nearly equal 

 to those of the fossil Amphistegina of the Vienna arid other tertiary 

 deposits. But Mr. Cuming's Philippine collection contains another 

 and far larger species, which is distinguished by the extraordinary 

 thinning-out of the last whorl ; and it is remarkable that in this 

 species the canal-system is highly developed, although completely 

 absent in A.gibbosa, a difference of structure, which, going along 

 with very close resemblance in external aspect and general confor- 

 mation, seems only to be accounted for on the supposition that the 

 difference in size requires a difference in the arrangement of the 

 nutrient apparatus. 



XXL "Further Researches on the Grey Substance of the 

 Spinal Cord." By J. LOCKHART CLARKE, Esq., F.R.S. 

 Received June 17, 1858. 



(Abstract.) 



In this communication it is proposed, for reasons assigned, to 

 divide each lateral half of the posterior grey substance into two 

 portions: 1. The caput cornus posterioris ; 2, the cervix cornus 

 posterioris. The caput consists of the broad or expanded extremity 

 of the cornu, and is separated from the cervix by an imaginary line 

 drawn across from the opposite anterior extremities of the gelatinous 

 substance ; the cervix comprises the remaining anterior portion of 

 the cornu. 



The caput cornus consists of two different portions : 1. an outer 

 and comparatively transparent portion, the gelatinous substance ; 

 2. an inner and more opaque portion, or base. 



1 . The outer portion or gelatinous substance consists of, 



A. Nerve-fibres, transverse, longitudinal, and oblique. 



B. Nerve-cells, large, small, and intermediate. 



C. Blood-vessels, and connective tissue, with numerous nuclei. 



2. The inner or more opaque portion of the caput cornus is con- 

 tinuous with the grey substance of the cervix, and surrounded 



2 A 2 



