166 Helen Dean King. 
of “intermediate forms” ultimately become males, and one also 
avoids the necessity of presuming that sex can be altered after an 
individual has completed its metamorphosis. 
In young toads, and possibly also in young frogs, primordial 
germ-cells that fail to undergo normal processes of development 
assume the characteristics of rudimentary ova, regardless of the sex 
of the individual in which they occur. An explanation of this phe- 
nomenon seems to me possible if one accepts for the amphibians 
Haeckel’s, ’74, view ‘“‘dass das dlteste und urspriinglichste Ge- 
schlechtsverhiltniss die Zwitterbildung war und dass aus dieser erst 
secundir (durch Arbeitstheilung) die Geschlechtstrennung hervor- 
ging.” In the male amphibian at the present time many of the 
primordial germ-cells still have the power, under certain conditions, 
of developing into ova which, since they cannot leave the sex-gland 
or come to maturity, are destined to degeneration and absorption. 
Except in very rare cases the primordial germ-cells in the female 
are no longer able to develop into spermatogonia. When, there- 
fore, these cells fail to develop along normal lines they become rudi- 
mentary ova which are similar in structure to the rudimentary ova 
derived from the primordial germ-cells in the male and they have 
a similar fate. — 
In adult amphibians, as a rule, germ-cells which fail to undergo 
normal processes at any stage of their development disintegrate at 
once and become absorbed. Some few cases have been found, how- 
ever, in which germ-cells in adult males have changed the course 
of their development and become rudimenary ova. Cole, 795, Fried- 
mann, 98, Latter, ’90, and Punnett, ’00, have noted the presence 
of rudimentary ova in the testes of various species of frogs, and I 
also have a preparation of the testis of an adult Rana pipiens which 
shows this anomaly. Rudimentary ova have also been found in the 
testes of adult Bufo vulgaris by Spengel, ’76, Moffmann, ’86, Knappe, 
’86, and Friedmann, 798, but as yet no cells of this kind have been 
found in the testes of the American species, Bufo lentiginosus. 
Fig. 4 shows a type of abnormality which is found occasionally 
in the sex-glands of young toads. The median genital ridge, which 
is usually divided into two ridges when a tadpole is from twelve to 
