702 



SCIENCE. 



[N. S. Vol. XXIII. No. 592. 



origin may be I am not prepared to say, but 

 they have no counterpart among birds and 

 ■with a few possible exceptions none among 

 other vertebrates. 



I may say that I do not regard them as the 

 result of mutation as the followers of de Vries 

 apparently do, but think it likely that they 

 may be due to the action of immediate local 

 environment, the exact nature of which it is 

 practically impossible for us to detect. The 

 extremely sedentary nature of plants, especially 

 some groups, and the ease with which isolation 

 may affect them would tend to emphasize the 

 effect of local environment in producing dif- 

 ferentiation. 



In terrestrial vertebrates we find among 

 snakes certain forms with peculiar coloration 

 occurring as colonies here and there within 

 the range of the species which do not conform 

 to any definite geographic habitat, and in some 

 fossorial or semifossorial mammals similar ex- 

 tremely local forms occur, as ' Geomys 

 colonics ' Bangs surrounded by the range of 

 Gr. floridanus and iuza and in just the same 

 sort of environment so far as we can see; 

 also ' Microtus rufidorsum ' Baird, which oc- 

 curs in colonies within the range of M. 

 pennsylv aniens. 



These may be parallel cases to those ex- 

 hibited in Viola, Crataegus, Aster, Panicum, 

 etc., and their sedentary nature seems to point 

 similarly to elements in the immediate local 

 environment as the probable cause of their 

 differentiation. 



WiTMEE Stone. 



Acad. Nat. Sciences, Philadelphia. 



isolation by choice. 



To THE Editor of Science: The recent dis- 

 cussion of isolation in Science reminds me 

 of a popular article I wrote for The Outlook, 

 emphasizing the psychic factor in evolution' 

 — the part that choice plays. We must, it 

 seems to me, not forget the various factors 

 that work together at the same time in pro- 

 ducing species. A fish with weak eyes would 

 naturally prefer cave life, and thus isolated 

 breed with others similarly equipped, phys- 

 ically and mentally. Those that have the 



'February 18, 1898. 



physical variation without the mental would 

 soon feel the effect of their want of sense. 



The same principle applies in protective 

 coloration. One may easily conceive of two 

 habitats where the protective coloration would 

 be quite different, and it is easy to see that 

 the survival of those sensible enough to stick 

 to the habitat best suited to them might 

 quickly lead to intensification both of the 

 tendency to seek the one habitat and of the 

 coloration that adapts them to it. Indeed 

 sexual selection may come in. Those having 

 a willingness to accept mates with an erratic 

 tendency to the other habitat or less protective, 

 coloration would have progeny less liable to 

 prosper. Thus we may easily imagine two 

 color races, species, arising, separated by a 

 hereditary preference for different habitats, 

 and for mates with all the peculiarities that 

 those habitats have produced, while yet there 

 is no physical barrier preventing the crossing, 

 which may indeed go on to some slight extent. 



Alfred 0. Lane. 



larval conger eels on the long island coast. 



The occurrence of larval conger eels in 

 great abundance on the Atlantic coast has, as 

 far as I am aware, not been recorded; ac- 

 cordingly the following note may be of in- 

 terest. 



On May 27, 1905, the ' Leptocephalus ' of 

 a conger eel appeared in great numbers at 

 Easthampton, on the south shore of Long 

 Island, about twenty miles from Montauk 

 Point. They were washed up by the waves, 

 literally, in thousands, and continued to come 

 ashore in greater or less quantity — being espe- 

 cially abundant again on June 3 — for about a 

 fortnight. It was evident that this interest- 

 ing harvest was due in some measure, at least, 

 to a local storm and change of currents, which 

 also brought in a number of bottom forms — 

 e. g., Natica and its eggs. 



The larvae were all of a uniform length of 

 about four inches, and in a few cases appeared 

 to be in normal condition; most, however, 

 were found to be either dead or dying. Dr. 

 Bashford Dean, who has seen my specimens, 

 tells me that they are probably Leptoceplialus 



