ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 307 



Determining Factors in Metamorphosis of Anura.* — P. Wintrebert 

 has experimented with tadpoles of Rana temporaria, and finds that tad- 

 poles of about 43 mm. long removed quite abruptly from the water to 

 moist air are not injuriously affected, and that in fact metamorphosis is 

 sharply accelerated. 



Portal Circulation in the Embryonic Metanephros of Mammals. t 

 Ivar Broman finds in the embryos of man, pig, and mole blood-vessels 

 in the rudiments of the metanephros. In a human embryo of 16 mm. 

 these were very distinct, as also in an 8 mm. mole and in pigs of 14-22 

 mm. It was suspected but not confirmed that the vessels branched off 

 from the arterial vasa efferentia of the primitive kidney. On the other 

 hand the author has traced some of these to the posterior cardinal veins, 

 and others to the venae revehentes of the pronephros. Hence it is 

 assumed that the kidney vessels found are all veins, and that the one 

 group is afferent and the other efferent. In other words, the meta- 

 nephros of the mammals examined very probably possesses at this stage 

 (before the kidney arteries have developed) a so-called portal circulation. 



Studies of Placentation.— F. MullerJ describes the pre-placentary 

 and placentary stages in the squirrel, and compares them with those in 

 other rodents. Hans Strahl§ gives an account of the uterus puerperalis 

 of the hedgehog, which is very distinctive, differing in many ways from 

 that of rodents. 



Bodily Identity of Twins. || — H. H. Wilder has made a study of 

 the ridge patterns of the hands and feet of twins. As the patterns are 

 ordinarily very variable he thought that they might illustrate the organic 

 agreement of the twin individuals more exactly than bodily form, physical 

 measurements, features, etc. He found a remarkable agreement, and 

 gives an illustration of the right hand of each of a pair of twins which 

 shows this in a striking way. While he admits that caution is necessary 

 in drawing conclusions, he suggests that in the case of twins resulting 

 from the bipartition of a siugle egg the agreement of the ridge figures 

 is due to the dominance of a determining substance within the egg, 

 which even here fixes the form they are to assume. The agreement is 

 only in the larger features and does not extend to individual lines, so 

 that the theory involves the notion that the details are determined by 

 forces acting later on in development. 



b. Histology. 



Structure and Function of Rectal Gland in Elasmobranchs.f — 

 Helen L. M. Pixell has studied the rectal gland, which Sanfelice and 

 Howes called the appendix digitiformis, in Scijlliam eanicula and Raja 

 punctata. It has a compound tubular structure, the walls of the tubules 

 consisting of low cylindrical cells interspersed with numerous goblet-cells. 



* C.R. Soc. Biol. Paris, lxiii. (1907) pp. 257-9. 

 f Anat. Anzeig., xxxi. (1907) pp. 94-7. 



X Proc. Acad. Amsterdam, Section of Sciences, ix. (190G) pp. 380-9. 

 § Op. cit., xiii. (1907) pp. 1-22 (3 pis.). 

 || Anat. Anzeig., xxxii. (1908) pp. 193-200 (2 figs.), 

 t Tom. cit., pp. 174-8. 



Y 2 



