9 
Recent Advances in the Study of Heredity. 
changes as a part of the general degeneration, and have become 
hermaphrodite in the one-time male. Many curious and unexplained 
sex-phenomena in the Cirripedia are explained very ingeniously by 
this theory. 
A remarkable case of protandry in the animal world, viz., in 
the slipper limpet, Crepidula fornicata, has been described recently 
by J. H. Orton. 1 This case illustrates and supports Smith’s theory 
of the origin of protandry extremely well, inasmuch as Crepidula 
fornicata is a Mollusc which had dioecious ancestors and which both 
phylogenetically and ontogenetically has adopted a sedentary life 
—and hence tends to degenerate--and also presents every con¬ 
dition between the earlier, purely male, and the final, purely female, 
condition. 
The observations on the phenomena of parasitic castration are 
thus seen to support the evidence derived from the Arthropods that 
the male is a Mendelian heterozygote and the female a recessive. 
We are now in a position to compare the different conclusions 
which have been held with regard to a Mendelian interpretation of 
sex. 
Male. Female. 
Castle ... DR ... DR ... Plants and animals. 
Correns ... DR ... RR ... Some animals and plants. 
Bateson ... RR ... DR ... One plant and some animals. 
Correns, it will be remembered, assumes a factor for mon¬ 
oeciousness, which is recessive both to maleness and femaleness. 
A study of the inheritance of sex indicates that for a number 
of animals and for one case among plants sexual phenomena are 
correctly described if the female be considered a Mendelian hetero¬ 
zygote and the male a recessive. On the other hand observations 
on cytological characters of a large number of Arthropoda, as well 
as the phenomena of parasitic castration in crabs, and the almost 
universal occurrence of protandry in animals,—all point to a gametic 
constitution the exact reverse of that just stated. The phenomena 
in parthenogenetic insects, however, indicate that a modification of 
Castle’s view may be nearer the truth for these cases. It seems 
too much to expect that these opposite views can be reconciled. 
Indeed it is hardly likely that sex-phenomena will be unified in one 
scheme ; for the evolution of differentiated gametes can be traced 
along several lines even in the lower organisms. It is therefore not 
reasonable to expect that sex should be inherited in the same 
1 Proc. Roy. Soc. B., Vol. 81, 1909. 
