Oll the Effect of Centrifugal Force on the Frog’s Egg. 
387 
the yolk-platelets to be composed of 6°/o of lecithin and 94% of batra- 
chiolin, a nucleo-albumin containing 1,2% of phosphorus, l,3°/o of sulphur 
and 15% of nitrogen ; and the fat droplets to be composed of a liquid fat, 
a solid fat melting at 58 degrees, and a yellow lipochrome. 
In the living frog’s egg, I have not been able to observe any struc- 
ture to the cytoplasm proper, that is, to the substance that fills the spaces 
between the yolk-platelets, fat droplets, and pigment granules. Gur- 
witsch (09) supposed an alveolar structure to exist, but which was ob- 
scured by the yolk-platelets. I examined younger ovarian eggs, contai- 
ning no yolk, fat or pigment, alive under a 2 mm oil immersion lens and 
could observe no structure in the cytoplasm except clumps of granules 
in certain regions, the yolk-nuclei. In a former paper (09, 1) in speaking 
Fig. 3. 
Fig. 4. 
The same structure as in fig. 2, 
in the OTarian egg of the toad, 
centrifugal force = 2771 X gravity 
for two hours. The greater visco- 
sity of the ovarian eggnecessitated 
a longer dnration of the force to 
obtain the same stratification. 
Portions cf cytoplasm in sections 
of ovarian eggs of Rana pipiens 
containing no yolk. 
of the alveolar structure of the normal frog’s egg, I referred to the spaces 
filled with yolk-platelets and fat droplets and containing in addition en- 
chylemma, as I supposed. It is hardly probable that spaces entirely occu- 
pied by yolk or fat can be rightly caUed alveoles in Butschli’s sense. 
If the frog’s egg be centrifuged, I observed (09,1) that the fat dro- 
plets rise to the top of the egg and fuse to form larger drops, whereas the 
cytoplasm proper forms a layer just beneath the layer of fat drops. A 
small portion of a section showing a part of each of these two layers is 
represented in fig. 2. Each layer has an alveolar or reticular appearence, 
the meshes in the fatty layer being larger than those in the layer below, 
which Gurwitsch calls artefacts. The meshes in the fatty layer are 
formed of the coagulated cytoplasm that separated the fat drops until 
the latter were dissolved out with xylol. The meshes in the layer below 
are probably artefacts as Gurwitsch maintains, but they are about as 
large as the meshes seen in the cytoplasm of fixed ovarian eggs contai- 
