466 CYCLOSTOMATA. 



and ripe spermatozoa, while older forms produce ova only, 

 and Nansen has corroborated this. Of the development 

 and early history nothing is known. They are said to 

 spawn in late autumn. 



Form. 



The body is eel-like, measuring 15-24 inches in the 

 adult. There is a slight median fin around the tail ; 

 beside the mouth and nostrils are four pairs of barbules. 

 There are no paired fins. 



The Skin. 



The skin is scaleless, and rich in goblet cells, which 

 secrete so much mucus that the ancients said the hag "could 

 turn water into glue." Besides the diffuse goblet cells, there 

 is a double row of glandular pits -arranged segmentally on 

 each side of the ventral surface along the entire length of 

 the animal. Each opens by a distinct pore. 



Muscular System. 



The muscle segments or myomeres are to some extent 

 traceable. Working the rasping teeth is a powerful 

 muscular structure, sometimes called a "tongue." 



The Skeleton. 



The skeleton is wholly cartilaginous. The notochord 

 persists unsegmented within a firm sheath, the skull is a 

 simple unroofed trough, jaws are not distinctly developed, 

 there is only a hint of the complicated basket work 

 which supports the gill pouches of the lamprey, but the 

 tongue, the barbules, &c., are supported by cartilaginous 

 rods. The end of the notochord in the tail is quite straight 

 (protocercal or diphycercal). 



Nervous System. 



The brain has the usual parts, but is small and simple. It 

 is much compressed, with practical obliteration of ventricles, 

 the fore brain seems to agree with that of Ganoids and 

 Teleosteans in having a non-nervous roof. The spinal cord 

 is somewhat flattened. Throughout at least a portion of the 

 cord there are two dorsal roots for each ventral root. The 



