1891.] Embryology. 755 
The eggs of Rana halecina are found still later, sometimes -in the 
same localities as the wood frogs, oftener in pools in the open ground 
quite away from the woods. The eggs are individually smaller, so 
that although the jelly masses are often as large as those of the woo 
frogs, the number of eggs is greater. The following are the records : 
March 2sth, April 5th, ’90. The eggs of Rana clamitans are not 
so certainly referred to its adult, and I have only strong probability 
showing them to belong to that species. The bunches much resemble 
those of Æ. halecina, but the eggs are larger and the jelly firmer. 
Those I have found were also attached to twigs of bushes, which 
is not always the case in #. Aalecina. 
The toad (Bufo lentiginosus) in this latitude lays very late in the 
spring. The eggs are easily distinguished from the frog’s, as they are 
laid in long strings, often yards in length, the eggs arranged 
(generally) in a single row. They were recorded April 14th, ’go, 
April sth and 6th, ’91. The best localities seem to be those parts of 
rivers or streams where the water backs up, and to one side protected 
by abar, so that the eggs are not carried away by the water, and where 
the water itself is often exceedingly warm. Copulating individuals 
are easily obtained, and they continue to lay in confinement. 
2. Laying in Confinement.—lIf frogs are caught at the height of the 
breeding season, they can often be got to lay in confinement. The 
surest way is to get the paired individuals, frightening them as little as 
possible, and placing them in dishes or aquaria containing the requisite 
amount of water. Only once have I had the wood frogs lay in the 
laboratory, although with proper precaution there seem to be on 
very great difficulties of obtaining in this way the eggs of this species. 
A single large bunch of eggs were laid by this pair during the night, 
which developed normally. 
By far the best and easiest eggs to be obtained by bringing frogs into 
the laboratory are those of the tree frogs named above. They will 
continue to lay small bunches of eggs for as much as twenty-four hours 
after catching them. By removing the bunches as fast as laid, an exact 
record may be kept as to the age of the different lots. Moreover, the 
eggs of these species are small and the jelly clear, so that they are 
well adapted for study of the segmentation stages under the micro- 
scope. The distinction between the cells derived from the black 
(animal) pole and those from the yellow (vegetative) pole is very 
sharp, and the fate of the cell® more easily traced through the later 
stages of segmentation. Toads brought into the laboratory and placed 
under proper conditions continue to lay for many hours. A single 

