18 PROCEEDINGS OF THE ACADEMY OF [1888. 



scraping, has also been resorted to, to increase the number of com- 

 mercial species. 



Hybridization may have been a factor in the origin of some va- 

 rieties as occurs in the allied genus Partula. The preservation of 

 the species in the lower animals is due in a great measure to animal 

 instinct, but where nearly allied species are thrown together, as often 

 happens in the involuntary change of position of Achatinella, or the 

 proximity of broods, as occurs with Partula, hybridization may take 

 place. It is well known that embryonic young are priceless to the 

 biologist, and since the tissue cells of species evolute from pre-exist- 

 ing germs and do not originate cle novo, the shape of the embryonic 

 or apical fold of each species of viviparous moUusk, should be the 

 true index of a species, except in the case of hybrids, when it would 

 take the form of one or the other of the parents, and would be far- 

 ther distinguished in the adult, by the form, size and color of the 

 predominating parent, a law always observable in hybrids. 



Dr. Isaac Lea has always maintained the importance of the shape 

 of the apical fold, for a correct determination of a species of IJnio, 

 I have said elsewhere, that viviparous hermaphrodite mollusca (being 

 ■cold blooded animals) would probably more readily hybridize than 

 warm blooded, which might in a measure account for the numerous 

 forms and varieties of Unionidse and Strepomatidse in the rivers of 

 the United States. The late Prof Haldeman believed that liybrid 

 Unios existed, and farther that individuals between Melantho decisa 

 sxnd M. ponderosa Qnj are often found, which look very much like 

 hybrids of these species. It is well-known that fish, frogs and toads 

 (which are cold blooded animals) hybridize, and recently some spe- 

 cies of salmon have been successfully and profitably hybridized. 



So far as known the food plants of the Achatinella have no in- 

 fluence in the coloration of the shell ; those species possessing a 

 black, dark or slate colored mantle, secrete a variegated shell, while 

 others with a greenish, bluish, light yellow or flesh-colored mantle, 

 secrete a shell with different shades of yellow. The varied and gor- 

 geous tints of the shells of Achatinelhe, are probably owing to the 

 action of light and oxygen on the secretions from the glands of the 

 mantle ; the striations and variations of color, are probably due to 

 the chemical composition of a fluid from a different set of glands ; 

 hence the painting of the arboreal species is more bright and pleasing 

 than that of the terrestrial, which are generally of uniform and somber 

 hues. The surface of all the porphyroid and gaily painted species, 

 exhibit under a glass, waved spiral striae, similar to Partuhe. These 



