540 SUMMARY OF CURRENT RESEARCHES RELATING TO 



spheres according to their parasitic relations are discussed. Plasmodia 

 may arise among the X-cells, and amoeboid cells may pass into the body 

 of the host. The spheres illustrate no mere inhibition of development, 

 but a peculiar divergence of development. The author discusses the 

 theoretical bearing of his results, especially on the recapitulation doctrine. 

 It is maintained that the actualization of potential characters in develop- 

 ment requires a more or less precise environment of nurture ; if that is 

 radically changed the organism may develop otherwise. 



Effect of Pituitary Substance and Corpus Luteum Substance on 

 Egg-production and Growth.* — Raymond Pearl continues his investi- 

 gation of this, and finds that feeding laying hens with the desiccated 

 substance of the anterior lobe of the pituitary body of cattle, at a time 

 of year when the rate of fecundity is declining, does not stimulate the 

 ovary to an increased rate of production. Growing pullets similarly fed 

 do not show any earlier activation of the ovary. Growing chicks 

 similarly fed show retardation in growth in body-weight, as holds in 

 Mammals also. Feeding with the desiccated substance of corpus luteum 

 brings about a retardation of growth about twice as great in amount as 

 that following pituitary feeding. Neither substance given to laying 

 pullets causes any retardation in the attainment of sexual maturity as 

 indicated by the laying of eggs. The birds so fed begin to lay eggs at 

 the same age as the controls, but with a smaller body weight. 



Winter Egg-production in Fowls.f — Raymond Pearl discusses his 

 experiments towards improving by selection the winter production of 

 eggs. The character is Mendelian in its genetic behaviour, depending 

 upon two factors, one of which is sex-linked. Mass selection for egg- 

 production (during the first ten years) was not effective, but selecti on 

 (during the last seven years) which was based upon the performance of 

 the progeny was extremely and quickly effective. The phfenotypic 

 variation of the character fecundity, in fowls, markedly transcends, in 

 extent and degree, genotypic variation. It is quite impossible in the 

 great majority of cases to determine with precision what is a hen's 

 genetic constitution with respect to fecundity from an examination of 

 her egg record alone. In this case, as in so many others, but in an 

 unusually pronounced degree, a sure diagnosis of genetic constitution 

 can only be made by means of the progeny test. If high-layers are 

 selected by the egg record alone, the breeder is not really selecting 

 genetically high-producers, except in a portion of the cases, and he 

 makes no progress in building up a highly fecund strain. To be effective 

 in changing the average productiveness of a flock of poultry, selection 

 must- pick out those birds as breeders which carry the factors for high 

 fecundity genetically, i.e. as an integral part of their hereditary make-up, 

 and not any other birds. 



Til ere is no evidence that the genotypes themselves were changed by 

 the selection. What the selection did was to change the constitution of 

 the population in respect of fecundity genotypes. Those individuals 



* Journ. Biol. Chemistry, xxiv. (1916) pp. 123-35. 

 t Amer. Naturalist, xlix. (1915) pp. 595-608. 



