424 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



any influence that tends to increase this value, whether in the gametes, 

 zygote, or developing embryo, favours or determines the production of 



the male condition. In over-ripe and under-ripe ova the ratio 



P 

 has a high value. 



Wilson points out that the central assumption rests on a very small 

 basis of fact, and he proceeds to show that even that small basis is 

 unconvincing. He concludes that Hertwig's theory is without real 

 foundation. 



Sexual Differences of Chromosome Groups.* — E. B. Wilson brings 

 forward evidence to show that " idiochromosomes " play a definite role 

 in sex production in Hemiptera. In at least • four genera, Lygceus, 

 Euschistus, Camus, and Podisus, both sexes show the same number of 

 chromosomes, but the small idiochromosome is present only in the 

 male. Stevens, it is pointed out, has independently made a similar 

 discovery in Tenebrio, so that the phenomenon is of wide occurrence in 

 insects. The author concludes that the heterotropic or "accessory" 

 chromosome has become unpaired in the male sex through the disappear- 

 ance in that sex of its mate, and regards this as a complete explanation of 

 the fact that in forms possessing the heterotropic chromosome the male 

 number is odd, and one less than the female number. He believes that 

 these facts may give the basis for a general theory of sex-production. 



Formation of Haemoglobin in the Embryo.f — L. Hugounenq and 

 A. Morel have studied in this connection the developing egg of the fowl. 

 Hgeniatogen, probably belonging to the paranuclein group, has at first 

 a number of functions in the egg. It contains, besides an albumen and 

 a ferruginous pigment (subsequently differentiated as haemoglobin), a 

 reserve of sulphur, phosphorus, carbonate of lime, and magnesia. 



Metamorphosis Independent of Nervous System.:}: — P. Wintrebert 

 finds that the larvae of Salamandra maculosa proceed normally with 

 their metamorphosis in spite of the destruction of a posterior portion of 

 the spinal cord and spinal ganglia. In spite of the absence of medullary 

 centres the tail of the larvae of Rana and Alytes exhibits the normal 

 phenomena of regression. 



Sexual Selection^ — A. Forel alludes to recent criticism, e.g. by 

 Groos || and Lameere f, of Darwin's conclusion that female animals 

 sometimes choose the more decorative males. He admits that there is 

 some justice in the criticism, but thinks that it tends to go too far. A 

 case in support of Darwin's position is given. A peahen that had never 

 seen a peacock was brought into the presence of one outside the breeding 

 season. She flew rather than ran to him in the greatest excitement, and 

 circled round about him in obvious admiration. He remained quite 

 cold and reserved until the advent of spring brought them together. 



* Journ. Exper. Zool., iii. (1906) pp. 1-40 (6 figs.), 

 t Comptes Rendus, cxli. (1905) pp. 848-9. 

 t Tom. cit., pp. 1262-4. 

 § Zool. Jahrb., xxiii. (1906) pp. 319-20. 

 i| Hessische Blatter f. Volksunde, iii. heft 2, 3. 

 ^[ L'Evolution des omements sexuels, Bruxelles, 1904. 



