430 Simon Henry Gage 



Whether these differences, which are mostly of degree, are 

 sufficient to constitute two different species, has been decided 

 in thenegative by Jordan, and also by Meek ('82, '85, '88). If 

 the criterion of natural and spontaneous interbreeding be taken 

 to settle the question, it must receive a different answer ; for 

 the lake lamprey, from its size alone would not form a mate to 

 the marine lamprey. Of course they are not upon the same 

 spawning grounds, but any one who has watched the spawn- 

 ing of lampreys, (see below under spawning) would, I feel 

 sure, agree with me that the difference in size is so great that 

 even if on the same spawning grounds, they would be mut- 

 ually incompatible. It is not asserted that it would be im- 

 possible to fertilize the ova of a marine lamprey with the 

 zoosperms of a lake lamprey and the reverse, but the criterion 

 of modern systematists is, not possible inter-fertilit\' under 

 very artificial conditions or by the intervention of man, but 

 the natural interbreeding under conditions to which both 

 forms have been subjected for many generations. * 



Now while I firmly believe that within comparatively recent 

 times, geologically speaking, the lake lamprey was a true 

 anadromous marine form it seems to me that at present, 

 judged by the physiological test of interbreeding, it would be 

 better to consider the lake lamprey a distinct species, and to 

 designate it either as Petromyzon utticolor DeKay, or P. dor- 

 satus Wilder, should the Lake Champlaiu larvae, upon which 



* For possible readers of this article who have not followed closely 

 the progress of views concerning classification and the nature of "a 

 species" it may not be out of place to add that by biologists (this 

 term including both morphologists and systematists) it is believed that 

 "species" as an entity in nature, has no existence as was formerly 

 taught, but that the arrangement of closely allied forms into groups or 

 "species" is largely for convenience. And as some criterion must be 

 used, the physiological one mentioned above seems to have gained the 

 greatest favor. 



As is shown in another article in this volume ( J. H. Comstock's), 

 while the practical aim of classification is to subserve convenience, its 

 true purpose is to show the phylogenetic relationships of organisms, and 

 the permanence of any system will depend directly upon the approxi- 

 mation with which this purpose is attained. 



