GERM CELLS OF ANURANS 239 
a rare condition and probably a result of defective thyroid devel- 
opment. The animals are abundant, are easily caught, and 
readily adapt themselves to laboratory conditions. Tadpoles 
caught in the autumn need not be fed more than once a month 
throughout the winter to keep them in good condition. First- 
season tadpoles rarely attain a greater length than 35 to 40 mm. ; 
second-season specimens average 65 to 85 mm. ; mature tadpoles, 
100 to 154 mm. It is rare to find larvae with a greater length 
than 145 mm., though the writer recently caught two male speci- 
mens measuring 159 and 165 mm., respectively, from snout to 
tip of the tail; both had ripe spermatozoa in the gonads. 
It will be shown later in this paper that the long larval life of 
Rana catesbeiana is correlated with a very interesting and sug- 
gestive phase of the germ-cell cycle — a phase which, while nor- 
mally occurring in other anurans and probably in many other 
vertebrate forms, is brief, and apparently obscured by other 
developmental phenomena, hence not so easy of interpretation 
as the same condition in the bullfrog larva. 
It should be stated here that there is apparently no seriation 
of germ-cell stages anteroposteriorly in the testis of larval or 
newly metamorphosed Rana catesbeiana such as has been 
described for various urodeles. The testis of a 40 to 50-mm. 
larvae is a narrow, flat, ribbon-hke structure, gray- white in 
color, somewhat convoluted, attached by a mesentery to the 
inner edge of the ventral surface of the mesonephros. It bears 
little resemblance to the testis of the adult and is longer than 
the gonads of newly metamorphosed frogs. The relation of 
the glands of first-year animals to those of second-year larvae 
and newly metamorphosed frogs is indicated in text figure 1. 
The internal structure of these gonads is indicated in photo- 
graphs (33 to 35, explanation of figures), where it will be readily 
seen that the center of the gonad consists of a large hollow (sec- 
ondary genital cavity) surrounded by a germinal epithelium con- 
sisting of a single or double layer of germ cells in 40 to 50 mm. 
tadpoles and of many layers of cells in 80 to 90 mm. animals. In 
mature larvae and newly metamorphosed frogs the central cavity 
of the testis is obliterated at definite intervals by migration of 
