52 



THE MUSEUM. 



lows: On April 2, 1898, I received 

 from my friend, Mr. H f E. Craven, 

 two living Limnuea, one L. stagnalis, 

 and the other L. auricularia. Two 

 days previously he had taken them 

 near Litchfield, in the act of conjuga- 

 tion, L. stagnalis performing the part 

 of male, L. auricularia, that of female. 

 The act was not observed to be reci- 

 procal. 



The animals were placed in fresh 

 water, and supplied with aquatic 

 plants, carefully freed from Mollusca. 

 The L. stagnalis, whose* shell had 

 been much damaged in transit, only 

 survived a couple days; but to my 

 great satisfaction, the other lived and 

 deposited two or three batches of eggs, 

 dying eventually on April 30th. The 

 young emerged from the eggs in about 

 a month's time, and were carefully 

 tended during the summer and autumn. 

 In the winter and spring they were 

 neglected owing to pressure of other 

 work, and but few survived. At the 

 end of June in the present year, these 

 had reached adult age, as was evidenc- 

 ed by the slight reflection of the outer 

 lip, and were killed without having 

 been observed to attempt reproduction. 

 Their shells exhibit some variation, but 

 show no affinity to either parent, for 

 all of their conchological characters are 

 quite unmistakably L. peregra. 



Now in connection with this case, 

 two points merit consideration. We 

 are at once confronted with the prob- 

 lem as to whether L. stagnalis, L. 

 auricularia and L. peregra are to be 

 considered as distinct forms, or as 

 mere races or sub-species of a single 

 species. Most conchologists, I doubt 

 not, would positively pronounce them 

 distinct, and those attentive and ex- 

 perienced students of the group, would 

 express a doubt. I do not propose to 

 enter into a long discussion upon the 

 value of various morphological differ- 

 ences as data for separating species, 

 but will merely emphasize the fact, 

 that no differences, conchological or 

 malcological, are sufficient to separate 

 two forms as distinct species, unless a 



sufficient number of observations are 

 made to prove that these differences 

 are constant, and that intermediate 

 forms do not occur to bridge over the 

 distinction. In the case of land and 

 fluviaiile Mollusca, with their extreme- 

 ly variable environment, we should ex- 

 pect to find great variation occurring, 

 variation becoming more and more 

 pronounced and permanent until at 

 last races or sub-species are produced 

 which no longer revert back to the 

 primative form, when they are re in- 

 troduced to earlier conditions of life. 

 (Such races are easily exemplified in 

 Homo sapiens.) Too often, unfortu- 

 nately, does the conchologist ignor the 

 scientific aspects of this difficult prob- 

 lem. Too often does he hasten to de- 

 scribe as a "new species" a specimen 

 presenting some trivial difference from 

 others occurring in neighboring local- 

 ities. Quite recently I noticed six 

 "new" species of Succinea described 

 from the Sandwich Islands alone, some 

 of them apparently based on charact- 

 ers such as specimens from different 

 localities often present in the case of 

 our S. putris. 



The remarkable progeny of the Lim- 

 naca just described appears to afford 

 phylogenetic evidence of considerable 

 importance. Everyone is of course 

 familiar with Charles Darwin's classi- 

 cal observations on the reversion of 

 the offspring of crossed breeds of pig- 

 eons to the primative stock. Have we 

 not here an analogous case? May we 

 not justly conclude that L. peregra 

 represents the primative form from 

 which have arisen L. stagnalis, and L. 

 auricularia, whether these are looked 

 upon as races or species. It seems 

 difficult to escape from such a line of 

 reasoning. 



We have printed these observations 

 in full, for we feel they are of consid- 

 erable importance, and may be the 

 means of some of our correspondents, 

 who have time at their disposal, and 

 ah inclination to work out some of 

 nature's secrets, to bring to light some 

 most interesting conclusions. For 



