8 PETER OKKELBERG 



that it takes place from August to January in Petromyzon 

 planeri. Gage ('93) believes it occurs about from August to 

 September or October in Petromyzon branchialis, and estimates 

 the time required for metamorphosis as probab'y ten to twenty- 

 six days. Reese ('00) found that larvae of the same species, 

 which were kept in the laboratory, metamorphosed about the 

 20th of October.' Schneider ('79) found metamorphosing larvae 

 of Petromyzon planeri as early as the middle of August. I have 

 found larvae of Entosphenus wilderi metamorphosing in the 

 brook during the months of August and September, but only 

 four specimens have been obtained; two on August 16th, one on 

 August 23d, and one on September 13th. No direct observations 

 have been made on the length of time required for metamorpho- 

 sis, but since adults have not been found during May, June, and 

 July, the three months following the spawning season; since 

 metamorphosing . individuals occur in late August and early 

 September while adults are obtained during the other months 

 of the year, it is likely that the usual time for metamorphosis 

 in this species is in August and September, and that it requires 

 only a short time. 



Entosphenus wilderi reaches its full length in the larval state. 

 After metamorphosis the germ glands grow very rapidly and 

 soon fill up the whole body cavity. The intestine atrophies and 

 becomes so smaU that it can be distinguished only with diffi- 

 culty in cross-sections of the body. After transformation no food 

 is taken by the animal. The whole metabolism of the body 

 seems to be changed and all the resources possessed by the indi- 

 vidual are used toward maturing the sexual products. After the 

 spawning season the adults die within a very short time. Dead 

 lampreys may sometimes be found along the stream, and cray- 

 fish have been found feeding on the dead bodies lying on the 

 bottom of the stream. 



It is remarkable that during the period of its adult life, extend- 

 ing from August or September to the following April, the lamprey 

 takes no food. During this time the germ gland ihcreases 

 greatly in size and most of the material for its growth must be 

 furnished by the fat body (corpus adiposum) and by the other 



