G. GENEKAL NATURAL HISTORY AND ZOOLOGY. 307 



been until lately a mystery. The anatomy of this fish has 

 been frequently investigated ; but it was not until the labors 

 of Cruvelli and Maggi that we have come to any thing like a 

 clear understanding of the process. The somewhat startling 

 conclusion is readied by these gentlemen that the eel is 

 strictly a hermaphrodite, and that eggs are fertilized by 

 sperm in the body of one and the same individual. Professor 

 Ercolani has repeated the experiments of the gentlemen 

 mentioned, and, while differing considerably in conclusions as 

 to the morphology and functions of the several parts, agrees 

 with them that eels are complete hermaphrodites, which we 

 may therefore consider as tolerably well established. Cruvelli 

 and Maggi find a very curious distinction between two spe- 

 cies of European eels the intestines in one being almost a 

 straight line, and in the other being very flexuose ; these dif- 

 ferences being accompanied by external peculiarities in the 

 relative position of the anus. 1 B^ October Q, 1872,9. 



INFLUENCE OF EXTERNAL CONDITIONS ON THE STRUCTURE OF 



INSECTS. 



In a paper by Dr. Horn upon the Coleoptera of the Rocky 

 IVIountains, published in Professor Hayden's report on the" 

 geology of Montana, an interesting generalization is made 

 in reference to the relations of external physical conditions 

 to the structure of insects. The doctor remarks that from an 

 examination of a large number of specimens oi Eleodes, as 

 also of other genera, he finds that the higher the elevation, 

 or the color of the climate, the rougher and more deeply 

 sculptured is the species, and that the smoother forms are to 

 be found at lower latitudes, or in places nearer the level of 

 the sea. For this reason lie has no difliculty in establishing 

 many so-called species of Eleodes and of Omiis as geograph- 

 ical races of a smaller number of species, and in which the 

 law referred to is clearly indicated. 



He also finds that species every where in our fauna appear 

 to be distributed on lines of country presenting as nearly as 

 possible similar meteorological conditions. Thus many Ore- 

 gon forms extend southward into California, gradually seek- 

 ino- a hio'her mountain habitat as the resrion becomes warm- 

 er. Two species Trogosoma harrisii and Phryganophilus 

 collaris extend their habitat from Maine to California, fol- 



