258 



Appendices to Fifth Annual Report 



35th, after which they decrease again. In a herring of 292 mm. (11 J 

 inches) total length, the 1st vertebra measured 1*9 mm. in length, the 2nd 

 was 2*6 mm., the nine succeeding measured 26 mm., giving an average of 

 3 # 1 mm. each; the following nine were 30'5 mm. long, an average of 3*4 

 mm. each; the next nine — the 21st to the 29th— equalled 32 mm., being 

 an average of 3*5 mm.; the 30th to 38th, 33*5 mm., being an average of 

 3-7; the 39th to 47th, 324 mm., average 3*6 ; and the 48th to 56th were 

 28*8 mm. in length, their average being 3*2 mm., — these figures including 

 the extremely narrow intervertebral portions. 



The first vertebra is more flattened from above downwards than the 

 others, which are almost circular in end outline, the first being elliptical, 

 and the notochordal perforation in it is not central, but considerably nearer 

 the dorsal surface. The anterior faces of the first and second vertebrae 

 are much flatter than their posterior faces and than both faces of the suc- 

 ceeding vertebrae. Indeed, in most cases there can scarcely be said to be 

 any hollowing of the anterior face of the first vertebra. The anterior end 

 of the largest vertebrae in the 292 mm. herring measured from 3*5 mm. 

 to 3 '8 mm. in diameter, the central perforation for the notochordal rem- 

 nant being *45 mm. in diameter. 



Where the greatest constriction of the notochord at the centre of the 

 vertebra occurs, the two deeply hollowed cone-like ends of the centrum 

 are connected by a perforation about \ the vertebral length and J mm. 

 in diameter. Externally the vertebral centrum follows this form, except 

 that it is subdivided by those ridges or septa lying both longitudinally and 

 transversely, which are the original centres of the circumnotochordal ossi- 

 fication. These, while in the adult scarcely projecting so far as the outer 

 edge of the terminal expansions of the centre, divide its external surface 

 into a series of sunk chambers, while, as will be described, certain of these 

 ossifications project to form articular processes. The arrangement of these 

 ridges or septa on the external surface of the vertebrae of the adult 

 herring, and which appear in the larval herring as primary bars of ossifica- 

 tion in the notochordal sheath, is as follows : — 



The under surface of the majority of the vertebrae is divided into two 

 chambers longitudinally by a median partition and by a latero-ventral on 

 each side. On each side of the centrum, and slightly below the median 

 line, is another longitudinal lateral septum, and on the dorsal surface of 

 the vertebra is a central chamber formed by two latero-clorsal ridges. These 

 ridges extend outwards from the narrow central portion of the vertebra 

 nearly to the plane of its ends, dividing it therefore into seven sunk 

 chambers— two ventral, two ventro-lateral, two dorso-lateral, and one 

 (median) dorsal — each of which, at the surface, is nearly the full length of 

 the vertebra, and sinks inwards to a point at the centre (PI. XVI. figs. 2, 3). 



In the pair of ventro-lateral chambers of the 3rd to the 24th vertebrae, 

 and wholly filling them up, lie or are fixed the basal pieces afterwards to 

 be described. 



The median ventral ridge becomes reduced about the 30th vertebra, and 

 gradually dies away until the 40th vertebra, where it has disappeared, 

 leaving in the vertebrae posterior to this a single median ventral con- 

 cavity.* 



There is in addition to, but less prominent than, these longitudinal 

 septa, one formed across the pair of ventral chambers, and this cross 

 partition is sometimes rather irregular in form, so as to give the under 

 surface of the vertebrae a somewhat reticulated appearance. 



In the first and second vertebrae these appearances are more varied. 



* This statement applies to the particular herring examined; slight variations have 

 been found to exist in others. 



