STRUCTURE OF LAMPREY 58 1 



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

 salmon, ProtopteruSy frog), and its muscles undergo a 

 granular degeneration (cf. Protopterus, tadpole, etc.). 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 may be slow. The young 

 are in many ways unlike the parents, and after 2-4 years 

 pass through a striking metamorphosis. To the larvae 

 before metamorphosis the old name Ammocoetes is applied. 



Form, skin, and muscles. — The body is eel-like, with 

 two unpaired dorsal fins, and another round the tail. 



The skin is scaleless, slimy, and pigmented. Its struc- 

 ture, like that of Myxine, is complex. Sensory structures 

 occur on the head and along the sides, and form a lateral 

 line system. 



The muscle segments or myomeres are well marked. 

 The suctorial mouth and the rasping " tongue " are very 

 muscular. 



The skeleton. — The skeleton is wholly cartilaginous. 

 The notochord persists unsegmented, but its firm sheath 

 forms rudimentary neural arches. The skull is imperfectly 

 roofed. There are no distinct jaws, but a cartilaginous ring 

 supports the lips of the mouth. There is a complex basket- 

 work around the gill-pouches, but it is not likely that its 

 elements correspond to visceral arches. Endoskeletal 

 cartilaginous rods, not comparable to the dermal fin-rays 

 of fishes, support the dorsal and caudal fins, and other 

 skeletal parts occur about the " tongue." The caudal end 

 of the notochord is quite straight. 



Nervous system. — The brain has the usual parts, but is 

 small and simple ; the roof of the fore-brain is composed 

 of non-nervous epithelium ; there is a distinct pineal 

 body, with hints of an eye ; the oral part of the hypo- 

 physis is developed from in front of the mouth, and 

 becomes closely connected with the involution of ectoderm 

 which forms the nostril. A unique peculiarity in the brain 

 is that the middle part of the roof of the iter is simply 

 epithelial. The spinal cord is flattened ; the dorsal and 

 ventral roots of the spinal nerves alternate and do not 

 unite ; there is no sympathetic system. 



Though the larva sometimes receives the name of *' nine- 



