618 J. PLAYFATR MOMUREICH. 



tebra. The canal for the spinal cord is larger than that struc- 

 ture; immediately above the cord a partition (fig. 14), down- 

 wardly pointed in the middle, projecting with the dorsal fissure 

 of" the cord, divides the canal into two portions, the lower of 

 which contains the central nervous system. The notochord 

 persists to a large extent. There are no ribs. 



A very close relation exists between the neural and pleural 

 processes and the dermal scales. These structures first make 

 their appearance as stout, tough, membranous plates, having 

 the same appearance as has been described for the membrane 

 plates in the roof of the cranium. In these membranes ossifi- 

 cation takes place, apparently concomitantly with that of the 

 neural and transverse processes, and the relations found in the 

 adult commence to show themselves. In a transverse section 

 (fig. 14) there is to be seen, astride, as it were, of the spinous 

 process, a plate — the dorsal scale (D. S.), and articulating with 

 the transverse processes very closely; there is, on either side, 

 a corresponding lateral scale (L. S.). 



These latter apparently take the place of ribs, acting as 

 protective structures to the organs within. 



IV. The Paired and UNrAiRED Fins. 



In Syngnathus the fins present are a fairly developed 

 dorsal, weak pectorals, and a caudal. In the young 

 stages an anal is present, which, however, does not pass 

 beyond the stage in which the fibrillation begins, but aborts, 

 and is entirely wanting in the adult. 



In Stage b (fig. 2) the dorsal fin consists of cartilaginous 

 rays embedded in the tissue of the body, and resting directly 

 on the membrane surrounding the spinal cord. The portion of 

 the fin outside the body is yet cellular, but a distinct fibrilhition 

 is present, which, increasing, results in the formation of the 

 horny rays. 



In Stage d (fig. 6) these have fully developed, their sui>porting 

 rays (I.C.) still being cartilaginous. Above, these are united by 

 a longitudinal bar, similar to what occurs in the paired fins of 



