no SCIENCE PROGRESS 



investigating such strains in finished articles. The measurement of the 

 dents needs a traveUing microscope magnifpng about 125 times and reading 

 to 'ooi mm. 



Dr. C. W. Metz has lately studied the chromosomes in two species of 

 robber flies, Asilus, and he has found an occurrence which seems to be of theo- 

 retical importance. In the ordinary zygote, as is well known, each kind of 

 chromosome is paired, one of each pair coming from the egg and one from the 

 sperm. In a cell generation before the ripe gametes are formed the 

 homologous members of the pairs come together in what is called synapsis. 

 Metz has found that Asilus is an exception to the general rule, for the homo- 

 logous chromosomes remain closely associated throughout the entire growth 

 period of the first spermatocyte, and there is an elimination of the leptotene 

 and zygotene stages. But true synapsis occurs in the telophase of the last 

 spermatogonial division. 



Professor C. B. Davenport, of the Eugenics Record Of&ce, Coldspring 

 Harbour, has been collecting statistics with regard to the heredity of twin 

 births. It appears that about i per cent, of human births are twin births, 

 but there are certain families in which the proportion rises to 5, 10, or even 15 

 per cent. There can be little doubt that in both man and such animals as the 

 sheep there are strains showing a special tendency towards the production 

 of twins. The study of twins is complicated by the fact that there are two 

 types, namely, twins derived from a double ovulation and twins derived from 

 a single ovulation, in the latter case there being a subsequent fission or 

 budding of the fertilised egg. Such single-egg twins are easily distinguished 

 clinically by being both enveloped in the same chorion, and they are always of 

 the same sex. Professor Davenport hi.s come to the conclusion that the in- 

 fluence of the male in twin production is determined by the circumstance that 

 twin production does not depend merely upon double ovulation, but upon 

 such a quality of the male element as shall result in a high proportion of 

 fertilisation of eggs ovulated and a small proportion of fertilised eggs containing 

 lethal factors. 



The New Zealand Journal of Science and Technology contains an interest- 

 ing article by Iklr. C. A. Cotton on Earthquakes in their relationship to the city 

 of Wellington. Wellington is built partly in the hollow and partly on the 

 hills surrounding this hollow. In some parts the hollow or lower ground is 

 very little above the sea-level, and it would need perilously little subsidence 

 to enable the sea to sweep over the land which was raised in the earthquake 

 of 1855. Moreover, as anyone will agree who has visited Wellington, there 

 are numbers of houses built upon the steep hills and cliffs around the city 

 which would be bound to suffer if and when a severe earthquake occurred. 

 Nevertheless, much of the evidence goes to show that the severe earthquakes 

 which have occurred within the memory of man have caused the land levels to 

 be raised rather than subside, and we trust that any further earthquakes which 

 may occur at WelUngton will be in this direction. 



The Australian opossum has become successfully acclimatised in New 

 Zealand, and it is surprising to learn that the present annual value of opossum- 

 skins exported from New Zealand is not less than ;^i5,ooo. Professor H. B. 

 Kirk, who has written a report on the subject, believes that the great alpine 

 range could well be stocked with a new brood of Tasmanian brown opossums. 

 It is said that the animals cause very little damage in the bush. 



Prof. R. Ruggles Gates has brought out in the New Physiologist a most 

 interesting and valuable paper on Mutations and Evolution. This article is 

 undoubtedly one of the most important contributions to the subject which 

 has been printed in recent years. The paper will be reviewed in the forth- 

 coming edition of Science Progress. 



The principles of racial subdivision for Europe, to-day, are the Nordic, 

 Mediterranean, and Alpine. It has been claimed that of these races the Nordic 



