THE LAMPREY. 469 



When the ova are freed from the ovary they pass into the 

 body cavity. Each has an oval horny case, with a circlet 

 of knobbed processes at each end. By these they beconne 

 entangled together. There are no genital ducts, and the 

 expulsion of the products requires to be investigated. The 

 development is still unknown. 



Besides Myxine glutinosa^ two other species are known, one from 

 Japan, another from the Magellan Straits. The genus Bdellostoma, from 

 Southern seas (off the Cape of Good Hope, &c. ), is nearly allied ; it has 

 six or more gill pouches which open apart from one another. 



Second Type of Cyclostomata. 

 Petromyzon — The Lamprey. 



There are three British species, the sea lamprey {Petro- 

 myzon marinus) over three feet in length, the river lampern 

 {P. fluviatilis) nearly two feet long, and the small lampern 

 or " stone-grig " {P. branchialis or planeri). They eat 

 worms, small crustaceans, insect larvse, dead animals, &c., 

 but they also fix themselves to living fishes and scrape 

 holes in their skin. As their names suggest, they also fix 

 their mouths to stones, and soQie draw these together into 

 nests. 



The spawning takes place in spring, usually far up rivers. 

 Before laying the eggs, the lamprey seems to fast (cf. 

 salmon, Protopterus, frog), and its muscles undergo a 

 granular degeneration (cf Protopterus, tadpole, &c.). Soon 

 after spawning the adults of both sexes die. For reproduc- 

 tion is often the beginning of death as well as of life — 

 though in higher animals the nemesis is often slow. The 

 young are in many ways unlike the parents, and after two 

 years or three years pass through a metamorphosis. To 

 the larvas before metamorphosis the old name Ammoccetes 

 is often applied. 



Form. 



The body is eel-like, with two unpaired dorsal fins, 

 and another round the tail. Two ridges, one on each 

 side of the anus, Dohrn compares to rudimentary pelvic 

 fins. Otherwise there is no trace of limbs. 



