ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 425 



Forel thinks that there was no question of any direct sexual excitement ; 

 the peahen was simply filled with a3sthetic transport at the novel sight 

 of such a beautiful cock. 



High and Low Dimorphism.* — G. Smith supplies data showing 

 that the differentiation of the males of many species of Arthropods into 

 high and low forms is of wide occurrence in distantly related groups 

 which show a high degree of sexual differentiation. The high and low 

 dimorphism may be facultative, as in those cases in which the low male 

 by growth passes through an intermediate condition to the high male ; 

 or definitive, as in those cases where growth ceases on the assumption of 

 the mature condition. The extent of development of the secondary 

 sexual characters, i.e. their " highness " or " lowness," is strictly corre- 

 lated with that of the primary sexual development. This latter is 

 largely influenced by particular conditions of life, e.g. by nutrition and 

 by the presence of particular parasites, and it appears that such in- 

 fluences have operated continuously in specific differentiation. As we 

 are here dealing with the reproductive organisation, there is not the 

 same a priori difficulty in the transmission of such affections as exists in 

 cases where the body only is influenced. 



Aortic Arches in Mammals.| — H. Lehmann finds that in both pig 

 and rabbit embryos six aortic arches arise. In the pig there is a com- 

 plete fifth arch on about the twenty-first day of development. There are 

 also two entodermal pouches between the fourth and sixth arches. The 

 rudimentary fifth in the rabbit, arising at about eleven-and-a-half days, 

 is less complete. Eemnants of the first and second transitory arches are 

 persistent in the pig, so that parts of six aortic arches exist simulta- 

 neously. The subclavians begin from the dorsal aorta and shift forward 

 in front of the union of the aortic roots. The pulmonary arteries arise 

 as symmetrical vessels from each sixth arch, and in the pig become 

 asymmetrical by union of the stems from both sides, reaching the con- 

 dition figured by Rathke. This is, however, a secondary condition, 

 their symmetrical origin having been pointed out by Bremer. 



b. Histology. 



Dual Force of the Dividing Cell.J— M. Hartog records a series of 

 experiments upon the forces of the dividing cell. His more important 

 conclusions may be briefly indicated. The cytoplasmic figure of the 

 dividing cell is a strain-figure, under the action of a dual force, analogous 

 to magnetism, and still more to statical electricity ; without prejudice as 

 to its nature, it is termed " mitokinetic force," or " mitokinetism." By 

 comparison with magnetic models, it is found that the spindle-fibres and 

 astral rays, the Hautschicht of the cytoplasm, the nuclear wall, and the 

 free chromosomes along the cell-spindle, must all be of high permeability 

 to mitokinetism as compared with the other structures of the cell. 

 Detailed comparisons with magnetic models are given. It is found 



* Mitth. Zool. Stat., Neapel, xvii. (1905) pp. 312-40 (2 pis. and 13 figs.), 

 t Zool. Jahrb. Abt. Anat., xxii. (1905) pp. 387-434 (4 pis.). 

 X Proc. Roy. Soc, Series B, lxxvi. (1905) pp. 548-67 (3 figs.). 



Aug. 15th, 1906 2 f 



