ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 303 



there may be {: repetitive species-making," when from the same stock 

 similar forms arise at different times and without being related to one 

 another, e.g. the To/a-types which arose from the Pectinid stock in the 

 Lias, again in the Cretaceous, and again in the Tertiary. 



Law of Reversion. * — Prof. Karl Pearson states the following 

 general results at the conclusion of a paper on the law of reversion : — 

 To) The laws hitherto propounded for blended inheritance do not appear 

 to cover the cases of exclusive inheritance, e.g. such cases as eye-colour 

 in man, coat-colour in horses or hounds, ivc. (6) The law of ancestral 

 heredity must be distinguished from a law of reversion. Neither seems 

 to fit the facts, if we adopt the amounts of heritage 1/4, 1/16, 1/32, &c, 

 from parent, grandparent, great-grandparent, &c, originally taken as a 

 first approximation by Mr. Galton. (c) That the mean correlation of 

 an n th parent with the offspring is one-half that of an (w — l) th parent 

 also appears doubtful. (This would follow if reversion were started from 

 the parent.) (d) Testing theory by the case of basset hounds, we find 

 much difficulty, owing partly to the great prepotency of the dam, and 

 partly to the large amount of artificial selection which is evidenced at 

 every turn, and obscures what may be termed the natural laws of inherit- 

 ance, (c) There is an urgent need to widely extend our knowledge of 

 heredity by new experiments and observations on other organs in dif- 

 ferent races. Facts are of the first necessity at the present time, and facts 

 collected on a large scale for a wide range. 



• Polydactylism in Poultry. f — E. Anthony notes that polydactylism 

 of the hind limb, rare among birds, is frequent in the gallinaceous tribe, 

 and especially in the common fowl. In all cases which he studied, 

 except one, it consisted in a duplication, or sometimes even in a tripli- 

 cation of the hallux. When the malformation is complete, there is a 

 superior hallux of 2-4 phalanges (as if sometimes reverting to a more 

 primitive state) and an inferior hallux of two phalanges. There is* also 

 a division of the tendons of the muscles of the hallux ; the short flexor 

 remains always normal ; the short extensor stops in extreme cases at 

 the top of the first hallux, the long extensor replacing it functionally. 

 The polydactylism arises from a division of the primordium of the 

 hallux. 



Development of Musculature of Reptiles.J — H. R. Corning has in- 

 vestigated the development of the muscles of the head and the anterior 

 extremity in Lacerta, his special object being the study of the history of 

 the mesodermic segments of the anterior part of the head, as contrasted 

 with the somites (primitive segments) of the posterior cephalic region. 

 His investigation confirms the view that these anterior mesodermic seg- 

 ments are primitive, and of more importance in the interpretation of the 

 cephalon than the secondary somites, which play a part in most verte- 

 brates in the formation of the occipital region of the skull. In other 

 words, he believes that the segmentation of the skull has nothing to 

 do with the segmentation of the mesoderm of the anterior part of the 

 head. 



* Proc. R. Soc. London, lxvi. (1900) pp. 140-64. 



t Journ. Anat. Physiol., xxxv. (1899) pp. 711-50 (25 figs.). 



X Morph. Jahrbuch, xxviii. (1899) pp. 28-104 (4 pis.). i 



