SEXUAL CHARACTERISTICS OF THELIA 609 
amount of either the base of melanin, probably tyrosin, or the 
oxidase, tyrosinase, or possibly to a decrease in both. It has 
been found that the amount of the ferment present has a great 
influence on the melanin produced (Kastle, ’09), increasing 
pigment production up to a certain concentration of the tyro- 
sinase, and then inhibiting the reaction. It is also known that 
even weak acids prevent melanic pigment production, and the 
parasites of Thelia probably bring about a condition of acidosis 
in the host, which has as its most important result fatty infiltra- 
tion of tissues, and which also may bring about inhibition of 
melanin formation. 
Recognizing that the metabolic level of parasitized male 
Thelia has been altered from the normal, are we to refer the 
changed morphological somatic characteristics as being due 
directly to this change? The answer to this question rests 
entirely on our conception of the origin and meaning of sex itself. 
If we believe that the underlying difference between the sexes is 
one of metabolism and not one of gamete production, then high 
metabolism has as its consequence maleness and sperm produc- 
tion, while low metabolism has femaleness and egg production 
as a consequence. The opposite view is that primarily the 
male is a sperm producer, the female an egg producer. The 
cells of an individual, somatic as well as germinal, are of one 
sex, either male or female. The metabolic level of the organism 
is merely one of the many expressions of sex, but a very impor- 
tant one in a consideration of gamete production and the nour- 
ishment of the offspring. This difference in metabolic pitch 
certainly is more important than other secondary sexual differ- 
ences, as size, pattern, coloration, or psychic characters, and 
probably preceded these in the phylogenetic development of 
sex. It has probably become more divergent in the two sexes 
as the gametes have been modified in evolution, as active seeking 
of the female by the male and internal fecundation has become 
established in higher forms and the development of the embryo 
has become dependent upon the female. Just as the form of 
the sperm or egg must be molded by the genes in the cells of 
the individual which produces them, likewise, it is not improb- 
