ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 131 



Hybridism between Cockatoos.* — Ernest Warren describes two 

 hybrids between Cacatua galerita (male) and Licmetis nasica (female). 

 Actual pairing was observed. Out of seven eggs, laid in three separate 

 years, only two hatched. The hybrids stand between the two parents, 

 but somewhat nearer to Cacatua than to Licmetis ; they illustrate the 

 blending of characters. Out of ten characters the hybrid is nearer to 

 Cacatua in five, nearer to Licmetis in one, and almost exactly inter- 

 mediate in four. In every character examined, with the possible excep- 

 tion of the coloured and non-coloured lores, there is a very obvious 

 blending of the male, and female characteristics ; and although the 

 external appearance of any hybrid is not to be regarded as an absolute 

 guide to its inherent gametic character, the evidence, so far as it goes, 

 points to a real blending of the characters of the parents, and the prob- 

 able absence of so-called gametic purity, or the segregation of characters 

 in their sexual elements. 



Hybridization Experiments on Fishes. f — Giinther and Paula 

 Hertwig have made a number of crosses, the varied results of which are 

 interpretable in terms of 0. Hertwig's theory of different degrees of 

 idioplasmatic disharmony between the paternal and maternal nuclei. 



Nearly related forms, e.g. Gobius jozo and G. capito, may be crossed 

 successfully and the viable though weakly offspring may be hatched. 

 But a crossing of G. jozo or G. capito and Grenilabrus pavo results in 

 the death of the developing ovum in the blastoderm stage or at the 

 commencement of gastrulation. 



Reciprocal crosses do not always yield the same results. Thus all 

 the ova of Grenilabrus pavo fertilized with sperms from a species of 

 Gobius die at the blastula stage, while the reciprocal hybridization 

 results in embryonic stages which attain to gastrulation of a pathological 

 sort. It is therefore necessary to recognize that the specific structure of 

 the germ-cells (the nature of the ovum-cytoplasm and deutoplasm) must 

 be taken into account. But the authors are not inclined to depart from 

 the doctrine of Hertwig and Strasburger that the idioplasm is nuclear. 



Development of Pronephric Duct in Elasmobranchs.J — George A. 

 Bates has enquired into this much-investigated subject, his material 

 being Acanthias embryos prepared by the vom Rath picro-osmo-platinic 

 method which renders cell-outlines and limiting membranes very distinct, 

 and makes it possible to differentiate between different cells and cell- 

 layers. This is all-important, for the main question is whether the 

 duct takes its origin in whole or in part from the mesoderm, or whether 

 it arises from or is contributed to by the ectoderm. The result of the 

 enquiry is to show that the primordium of the duct is a direct outgrowth 

 from the pronephros, and therefore mesodermic in origin, that its subse- 

 quent growth is accomplished by the division of its own cells, and that 



* Annals Natal Museum, iii. (1914) pp. 7-28 (1 pi.). 

 t Arch. Mikr. Anat., 2te Abth. lxxxiv. (1914) pp. 94-88 (1 pi.). 

 % Journ. Morphol., xxv. (1914) pp. 345-72 (5 pis.). See also Tufts College 

 Studies, iv. (1914) No. 2, pp. 345-72 (5 pis.). 



