452 Shu on He^iry Gage 



of the scientific world dates from the discoveries and the pub- 

 lication of A. Miiller, 1856. (See note on p. 437 above). 



Duration of the Larval Period. — The time required for the 

 larva to prepare itself for adult life is not known. It has been 

 estimated at three to four years. The reasons for assigning 

 that time are : The larvae that may be obtained from the 

 natural habitat at any season of the year are of such varying 

 sizes that it is believed that from three to four generations are 

 represented. The first of September for example, one may 

 obtain from the same bank or bed, as the fishermen call 

 it, lampreys in various stages of transformation, larvse 

 about two-thirds as large as the transforming ones and so on 

 down to the generation of that year, which are from 15 to 40 

 millimeters in length. This like the supposed death of the 

 adults after spawning is one of the questions that must be de- 

 termined experimentally. As the larvae are easily kept for 

 six months to a year in an aquarium with sand, it would doubt- 

 less be very easy to keep them from the &%% until transfor- 

 mation, by imitating closely the conditions obtaining in their 

 native home. 



Transformation and Duration of Adult Life. — When the 

 larvae attain a length of 120 to 160 miUimeters for the lake 

 lamprey or sometimes as great a length as 200 millimeters for 

 the brook lamprej^, they transform to the adult condition. 

 The brook lamprey does not apparently increase in length 

 after transformation, for many of the transformed ones at the 

 spawning season are of less size than the just transformed 

 ones. There is, however, some increase in the bulk of the 

 body, and a considerable increase in the gonads. As shown 

 in plate vii, figures 35 and 36, the ova and the sperm mother- 

 cells are in about the same stage of development as the lake 

 lamprey six months before spawning. It is believed from this 

 that the brook lamprey attains nearly its full growth before 

 transforming, and that the free life in the water is only about 

 six months, that is from the transformation in the autumn, 

 August and September and perhaps October, till the following 

 May. 



The lake lamprey upoii transforming is only about \ to 



