SUMMARY OF CURRENT RESEARCHES. 5 



of oestrus, most, if not all, of the older and many younger follicles then 

 undergo degeneration, and this may result in more or less persistent 

 sterility. 



Other causes may induce degeneration of ova, chiefly nutritive 

 causes and competition. Ova may be constitutionally incapable of 

 utilising the nutriment which is supplied, and on which other neigh- 

 bouring ova flourish. 



When young ova degenerate under such conditions, there is a great 

 probability that in these cases the degeneration is due to peculiarities in 

 the constitution of those ova, and that such ova require special facilities 

 for development. They may give rise to " sports." It is reasonable to 

 expect that, given the requisite quality of nutriment, the power of 

 producing variable offspring would be widely extended, and the field for 

 the study of variation correspondingly enlarged. 



There is increasing evidence that the ovary is a secreting gland, 

 essential to the normal functions of the rest of the system, and to the 

 normal development of sexual characteristics. There is probably a 

 special generative ferment, or " gonadin," which exercises through blood 

 a profound and far-reaching influence on the organism. 



Chromosomes in Relation to Determination of Sex. * — E. B. 

 Wilson has found that the sexes of Hemiptera show constant and 

 characteristic differences in the chromosome groups. The cells of the 

 female may have one more chromosome than those of the male, or one 

 of the male chromosomes may be smaller than the corresponding one in 

 the female. In the first case the spermatozoa are of two classes, one of 

 which contains one more chromosome (the so-called "accessory," or 

 heterotropic chromosome) than the other. In the second case all the 

 spermatozoa contain the same number of chromosomes (half the soma- 

 tic number), but they are, nevertheless, of two classes, one of which 

 contains a large and one a small " idiochromosome." It may be that 

 fertilisation by spermatozoa with one chromosome wanting, or with a 

 small idiochromosome, results in male offspring. 



Egg 7 + spermatozoon - = n (female). 



Egg - -f- spermatozoon - — 1 = n — 1 (male). 



It may be that the difference between the two types of germ-cell is a 

 matter of metabolism, primarily one of growth. 



Resistance to Temperature in Frog's Eggs.f — E. Bataillon finds 

 that the resistance to the influence of temperature increases in the 

 course of embryonic development. It is very marked towards the 

 closure of the blastopore. The unfertilised egg is more resistant than 

 the fertilised egg. The spermatozoa in the seminal vesicles are more 

 resistant than the ova in the lower part of the oviducts. The abnor- 

 malities seem to be traceable to a modification of the plasma of the 

 ovum. 



* Science, xxii. (1905) pp. 500-2. 



t Arch. Zool. Exper., iii. (1905) Notes et Revue, ccxii.-ccxv. 



