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754 The American Naturalist. [August, 
jelly membranes. At last I think that I have successfully solved the 
problem, and can now obtain with the greatest ease the most difficult 
stages, which are also in perfect histological condition. The method 
will be given in the last section—g. Clay models of the early stages 
of segmentation of the egg have been a very useful addition in pre- 
senting to others the arrangement of the cells. These, of course, 
should be copied from actual eggs, and not from the perfectly regular 
(but entirely schematic) figures of the ordinary text-books. 
The following topics are touched upon: (1) Time of Laying, and 
Localities. (2) Laying in Confinement. (3) Polar Bodies. (4) Seg- 
mentation of the Eggs. (5) Orientation of the Egg. (6) Enclosure 
of the Light Pole by the Dark Pole. (7) Effect of Temperature. 
(8) Times of Hatching, etc. (9) Methods of Technique. 
1. Time of Laying, and Localities. —The observations were made in 
the vicinity of Baltimore, Md., during the spring months of the years 
’88, ’89, 90, 91. I shall only speak of those species of whose iden- 
tity I am certain. Other and more imperfect observations are left out, 
The first frogs to lay, and amongst the very first (Acris gryllus excepted) 
to appear, are the wood frogs (Rana sylvatica). A few warm days in 
early spring suffice to bring them out. The following records give a 
general idea as to the time: February 23d, ’91, and March 8th, goth, 
and roth, ’80. The eggs of these had been laid several days. The egg- 
bunches are found in small pools on the edges of woods, generally 
amongst the low hills, and are often stuck to twigs of bushes. The 
bunches are generally large, four to six inches in diameter, and contain 
very many good-sized eggs. In the same pools it is quite usual to find 
the firmer egg-bunches of Amblystoma, as this Urodele also lays its eggs 
very early. 
Somewhat later two species of tree frogs appear in the small pools 
in the woods, generally in quite small, and therefore, during the day- 
time, often quite warm, puddles; sometimes in the same pools as the 
wood frogs, oftener in the ditches by the side of the road. These tree 
frogs are Hyla pickeringit and Chorophilus triseriatus. They are often 
found paired, and may be in this condition carried to the laboratory, 
where they continue to lay for hours without abatement. The eggs of 
these species are very similar, and I know no certain method of dis- 
tinguishing the one from the other. The bunches are small, attached 
to bits of grass, or lie simply on the bottom, and each bunch contains 
from five or six to fifteen or twenty eggs. I have the following records 
of times at which the eggs were found: Hyla—March oth, roth, 13th, 
_ April M "go ; Chorophilus—February 23d, ‘91, March 13th and 
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