420 SECTIONAL TRANSACTIONS.—C, D. 
in later times. The group includes, for example, the ‘ Charnockite-Anorthosite 
Series’ of Rosenbusch, and also the large magnesian intrusives commonly 
associated with this series. 
10. Mr. H. H. Reav.—The Contaminated Magmas of Aberdeenshire. 
SECTION D.—ZOOLOGY. 
(For references to the publication elsewhere of communications entered in 
the following list of transactions, see p. 465.) 
Thursday, September 8. 
1. Presidential Address by Prof. IK. S. Goopricu, F.R.S. See 
p. 79. 
2. Joint Meeting with Section K. Discussion on Forest Insect Pro- 
blems. See p. 451. 
3. Dr. F. A. E. Crew.—The Mechanism of Sez-reversal in Frogs 
as illustrated by the Recorded Cases of Abnormality of the 
Reproductive System and by the Results of a Breeding Experi- 
ment. 
The cases are arranged so that they form a complete series beginning with 
an individual which in primary and secondary sexual characters and in accessory 
sexual apparatus is an almost perfect female, and ending with one which is an 
almost perfect male. It is shown that the process is initiated by the appear- 
ance upon the inner border of what hitherto has been a typical and functioning 
ovary of a nodule of spermatic tissue. In such an ovo-testis the ovarian tissue 
degenerates and becomes removed, whilst the spermatic thrives until the gonad 
assumes the form and structure of a typical testis. Simultaneously the in- 
dividual develops the secondary sexual characters and accessory apparatus 
of the male, and the only female character which persists is the Millerian 
ducts of a size equal to that of the oviduct of the adult female. Such an 
individual functions as a male. One such fertilised the eggs of a normal 
female, and every one of the offspring reared to an age at which the sex could 
be identified proved to be a female. This is what one would expect if the 
chromosome constitution of the frog is of the XY type, for an XX ¢ mated 
with an XX 2 would produce a generation all XX in chromosome constitution. 
4, Rutn C. Bamerer (Mrs. Brspex).—The Male Tortoiseshell Cat and 
a Suggestion on Sex-determination. 
Male tortoiseshell cat.—No case of confluence of blood-vessels found in 
embryo cats. Two records of tortoiseshell males from otherwise female 
families. Thus parallel with freemartin, suggested by Doncaster, seems 
improbable. But tortoiseshell male may be case of sex reversal at fertilisation. 
Cf. Riddle’s pigeons, Goldschmidt’s and Harrison’s moths. (I believe that 
Dakin thinks tortoiseshell male comparable with Goldschmidt’s intersexes.) 
Difference between yellow male and tortoiseshell female possibly due only to 
sex physiology; if tortoiseshell male an example of sex reversal physiology 
probably incompletely male (cf. usual sterility), then tortoiseshell coloration 
expected. 
Sex-determination.—Suggestion that sex due to metabolic rhythm, male 
and female metabolic conditions tending to alternate; cf. chemical rhythms. 
At fertilisation metabolism turned in either direction according to relative 
“strengths” of germ cells. Chromosome content, and sex, possibly parallel 
results of metabolic condition. Avoids split in living universe made necessary 
by X chromosome hypothesis. : 
5. Prof. J. ArrHur Tnomson.—Are there ‘ Modification Species’ ? 
An Antipatharian colony with which a Polychet worm is associated departs 
altogether from its ordinary mode of growth and forms a basket-work tunnel 
in which the worm lives. Similarly, in a Primnoid colony, the presence of a 
