ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 659 



different in rats and in guinea-pigs, yet a careful analysis of the facts 

 shows the results to be not so dissimilar in the two cases as they at first 

 sight appear. In both types the average extent of the pigmented areas 

 can be increased or decreased at will by selection. The pigmented areas 

 vary in extent continuously, and from these variations permanent modifi- 

 cations of the pigmentation can be secured. In guinea-pigs the authors 

 attempted by selection to restrict the number of the pigmented areas ; 

 this was found to be impossible except as it occurred incidentally to 

 reduction in the total amount of pigmentation. The regression occurred 

 in number of pigmented areas, not, so far as known, in the total amount 

 of pigmentation. Such regression occurred, however, where extreme 

 variates were selected, e.g. in selecting black-eyed white guinea-pigs. 

 Almost invariably such animals have borne more pigment than did their 

 parents. The authors are inclined, however, to qualify de Vries' opinion 

 that the effects of selection are not permanent, and consider the question 

 still an open one. They incline to think selection is a most important 

 factor, not only in the isolation of discontinuous variations but also in 

 their production. A sharp Une of distinction cannot be drawn between 

 continuous and discontinuous variations. The hooded and Irish coat- 

 patterns of rats are recognised discontinuous variations, alternative in 

 inheritance, yet the authors had a lot of hooded rats (Lot M) un- 

 doubtedly intermediate between the two types. The coat-patterns of 

 fancy rats, though discontinuous as they ordinarily occur, can be trans- 

 formed into continuous variations. It is impossible to make a sharp 

 distinction either here or between blending and alternative inheritance, 

 and it is consequently " fallacious to assign all evolutionary progress to 

 one sort of variation or to one sort of inheritance." 



Determinate Variation.* — Vernon L. Kellogg, in an interesting paper, 

 discusses the case of the " Californian flower-beetle " DiahroUca soror, 

 which in the neighbourhood of Stanford University is "changing its 

 spots." Statistics are adduced showing that in this region, but neither 

 at Santa Rosa which is sixty miles to the north, nor at San Jose twenty 

 miles soutli, D. soror has changed from a form whose elytra have twelve 

 black spots on a green ground to one of eight spots free and two 

 in-egular transverse blotches in place of the middle four spots. An 

 analysis of the case has led the author to conclude that the change is 

 not an ontogenetic one, nor is it to be attributed to natural selection. 

 The variations are of the small continuous type. The author concludes 

 with the question : " Is there determinate variation ? " Or in other 

 words, is there progressive variation of a cumulative character — 

 " determinate or orthogeuetic " — -which is independent of or antecedent 

 to selection ? 



Development of Sympathetic Nervous System in Mammals.f — 

 A. Kohn has investigated this subject in the rabbit. The cells of the 

 primordium are neither directly separated off, nor do they migrate from 

 the spinal ganglia. They arise from the ramus ventralis of the spinal 

 nerve. Embryonal neurocytes deviate from the course of the mixed 



* Science, xxiv. (1906) pp. 621-8. 



t Arch. Mikr. Anat., Ixx. (1907) pp. 266-317 (3 pis. and 3 figs.). 

 Dec. 18th, 1907 2 x 



