RELATIVE STRENGTH OF 11EREMTARY INFLU ENCES. The three following conclusions rest on an elaborate series of experiments by Stand fuss with three European species of Saturnia moths: (1) The freshly hatched hybrid larva closely resembles that of the female parent, but with the process of growth a resemblance to that of the male parent gradually increases.
(2) The extent of approximation toward the male parent depends on the relative phylogenetie age of the two species, the older being able to transmit its properties, whether of structure or habit, better than the younger.
(3) In reciprocal pairing, the male is able to transmit the characters of the species in higher degree than the female. This influenee, however, is less regular and potent than that spoken of in the preceding paragraph.
The result of crossing cc parent spreirs with a local rare, or with an aberration of the same spe cies, is as follows: (1) When the normal form of a species ( Grand art) is crossed with a gradually formed local race of the same species, the result is a series of intermediate forms. (2) On the other hand, when the normal form is crossed with a sporadic aberration, the result in many cases is that the issue divides itself sharply between the normal form and the sport. intermediate forms being absent.
In commenting on these results. Dr. F. A. Dixey remarks: (1) The experiments afford fresh illus trations of the manlier in which the physiological isolation of an ineipient species may be brought about. (2) They show that the statement of Focke as to the .great variability of the offspring resulting from the crossing of a plant hybrid with one of the parent species holds good in the ease of insect a. (3) What Standfuss speaks of as the prepoteney of the phylogenetically older of the parent species is probably only another expression of the principle established] by Dar win that in many eases crossing causes reversion to a remote ancestor. (4) The general conclu sion as to the prepoteney of the male parent ac cords so far with one result of Calton's invcstiga lion of the late Sir E. \lillais's breed of basset hounds. (5) The result of crossing a parent spe cies with a gradually formed local race. though less in degree. is much the same in kind as that of crossing two distinct species. (6) The result of crossing the normal form of a species with a sporadic aberration of the same species appears to show that the latter stand biologically on an entirely different footing from the regularly de veloped variety, even though it may indicate (as alleged by Eimer and li• Jordan) the direc tion in which variation for that species is pos sible. With Standfuss's instances may be com pared the well known case of the 'otter sheep,' which similarly, when crossed with it sheep of ordinary breed. gave no true intermediates. (7)
Certain experiments with ;iberrations of this kind, of which exact numeric-a] records have been kept for several generations, ;ire of special inter est in connection with Otilton's law of heredity. (;a114)11, Natural Inheritance, p. 134 (Lon don, ISSN.
In still later experiments by :-:tstrulfuss (1s98) he shows that the crossing of two distinct species gives rise to a zwischen/oral, but not to a mit/a /or/id. The latter may. however, exist as a porary stage in larval growth. This depends on the following principles: (I) The freshly hatched larva closely resembles the female parent: (2) with the process of growth a resemblance to the male parent gradually increases: (3) the final extent of approximation toward the male parent depends on the relative phylogenetie age of the two species, the older being able to transmit its properties, whether of structure or habit, better than the younger: (41 in reciprocal pair ing the male is able to transmit the characters of the species in a higher degree than the female: (5) when the normal form of a species It;ruml art) is crossed with a gradually formed local race of the same speeies, the result is a series of intermediate folios: 16) when the normal form is crossed with a sporadie aberration, the result in many eases is that the issue divides itself sharply between the normal form and the sport, intermediate forms being absent.
I hence. according to Stand fuss, adds Dixey, "the process of species formation must be gradual; for when two distinct species are crossed the issue Hoes not split up into two parental forms, as in the case when one parent is a suddenly formed aberration. On the contrary, the behavior of the issue of two distinct species is very similar in kind to that of a species with a local race or variety which is being gradually estab lislid.d by the accumulation of slight changes. Tt would seem, therefore. that although an aberra tion or sport may he perpetuated by inheritance, it can never acquire distinct specific rank. No doubt, however, it may, if selected, eventually replace the original form of the species." Dixey also makes the interesting suggestion that these sporadic color aberrations "seem to have many points of resemblance with the color varieties in ddimestie animals, such as the 'lemon and white' and 'tricolor' of the basset hounds, or the well-known tortoise-shell. tabby, and blaek of eats. The fact that these domestic varieties exist side by side in the same race, and even in the same litter, and that true intermediates are rare or absent, seems to suggest that they orig inally appeared as sports. and that their per petuation has been insured or favored by artificial select ion."