Summary. A description is given of an experiment to find out whether or not fowl spermatozoa are susceptible to temperature shock. Evidence was obtained that there is no significant decrease in the fertilizing power of fowl spermatozoa when the semen is exposed to a rapid fall in temperature at the time of collection.

A literature review on chicken blood groups provides ample evidence in support of an association between red cell antigens of chickens and performance traits of economic importance such as egg production, hatchability, weight of chicks at 9 to 10 weeks, and liveability of progeny, (see reviews by GILMOUR [1960] and BRILES [1964]). This evidence indicates a selective advantage of heterozygosis for blood group genes. The purpose of the present paper is to record further evidence of a similar advantage of heterozygosis at blood group locus L in either parent for fertility. MATERIALS A N D METHODSChickens used in this study were from a highly inbred linz of White Leghorns, called the R line, described by PEASE (1948), and maintained by annual brother-sister matings at the Agricultural Research Council Northern Breeding Station at Reaseheath, Cheshire, England. According to the blood type at the L locus it was possible to arrange the following four mating combinations using 16 cockerels and 48 hens allocated to them at random: (1) heterozygous males X heterozygous females (L'L2 X L'LZ), ( 2 ) heterozygous males x homozygous females (L'L9 X L*L2)), (3) homozygous males x hetzrozygous females (LgLz x L'LZ), (4) homozy-gous males X homozygous females (L*L* x LzL*).