THE FROG 65 
tion to the bile sac, pancreas and intestine require special atten- 
tion. Using a large frog, make a preparation showing the organs 
represented in figure 42 of Holmes’ Biology of the Frog. The 
parts should be pinned out on a wax plate, such as is used for 
dissecting trays, which may be made as follows: Melt some bees- 
wax, soft commercial paraffin, or a mixture of these two sub- 
stances and stir in sufficient lampblack to color it an intense 
black; pour out into a shallow tray enough of the mixture to 
form a layer about 8 millimeters thick, and allow it to.cool. The 
plate may then be cut to the required dimensions. The prepara- 
tion should be exhibited in a rectangular glass jar containing 
alcohol rather than formalin, since the latter will attack the pins. 
For fastening the preparation to the wax plate, porcupine quills 
have some advantages over metallic pins. 
B. The Urogenital System.— Using fresh material, make prep- 
_arations of the reproductive systems of a male and a female 
frog by exposing the organs so far as possible im situ. The 
bladder should be injected with gelatin. In the case of the female, 
the ovary of one side may be removed in order to display the 
other organs to better advantage. Since in the female, especially 
if taken during the breeding season, the oviduct readily absorbs 
water causing it to swell to an inconvenient size, the use of 
formalin for hardening and preserving this preparation is not 
advisable; the dissection should be placed directly in alcohol. A 
similar preparation should be made of the female reproductive 
system showing the eggs in the uteri; females in the right condi- 
tion for this preparation may be found in the early spring. 
Of greater importance than the above is the making of perma- 
nent preparations showing the urogenital system removed from 
the body so that all its parts may be separated out clearly and in 
particular the ducts shown in their relation to the cloaca. The 
figures in Leuckart’s charts on the anatomy of the frog (Kny 
Scheerer & Co.) will best serve as a guide in making these prepa- 
rations. Using fresh material, remove the urogenital system 
entire, together with the large intestine and especially the cloaca, 
as follows: Dissect the bladder free from the posterior body wall, 
cut the cloaca across as far back toward the anus as possible, 
dissect the entire large intestine free from the dorsal body wall. 
