154 



BIOLOGICAL LECTURES. 



tive of variation than the shallower waters of inland basins or 

 the surface of the land itself. Hence so far as the effects of 

 g-coirraphical distribution are concerned, they may be said to have 

 had very little or almost no effect upon the anatomical structure 

 of the animal. This conclusion is fully sustained by the fact 

 that in each locality Bdellostoma shows similar variability in 

 the same organs, while individuals from widely separated 

 localities show variations which are frequently numerically 

 identical. The variability is of the same kind and comparable in 

 deeree in individuals from all the localities yet studied. This 

 is by no means a satisfactory presentation of the effect of 

 geographical distribution, but it must suffice for the present, 

 and until our knowledge of the distribution of the animal has 

 been more fully elucidated. 



What effect should these facts have upon our ideas of the 

 classification of Bdellostoma.' Most authorities are inclined to 

 look upon the difference in the number of gills as a sufficient 

 ground for the establishment of distinct genera. That this 

 character has not a generic value it is needless to state, for 

 reasons already sufficiently repeated. But it would be conven- 

 ient to recognize these several varieties by some name, if 

 possible, and, according to the present system of nomenclature, 

 there are tv*^o opportunities, — one for a specific, the other 

 for a variety name. Is the gill variation a sufficient specific 

 character .!" I think not, for the reason that we have all 

 p-rades of the variations, and the further reason that the\- all 

 belong to one colony of freely intercrossing individuals. It 

 appears to me by far the best plan to recognize one genus 

 of Bdellostomids, with one species composed of the several 

 varieties, and I propose that we return to the first satisfactory 

 name that was applied to our animal. The first account of 

 this animal which we find in the literature is that of Lacepede, 

 who described it from a dried skin sent from the Chilian coast. 

 He named it le Gastrobranche dojnbey} Later, in 1815. Home 

 described the gills of a Ileptatrema which he obtained from 



1 Gastrobranchus is the old name applied to My.xine, and these forms were kept 

 with Myxine till Dumeril put them in the genus Heptatrema, which of course 

 gives this name priority over Mulkr's Iklellostoma. 



