530 THE AMERICAN NATURALIST: (VoL: XXXIII. 
Blood Spots in Hens’ Eggs. — Every one is familiar with the fact 
that flecks of blood are occasionally seen on the surface of the yellow 
of a perfectly fresh hen’s egg. It is evident that these flecks are 
derived from some maternal structure and are not a product of the 
development of the egg, as they are present before incubation begins 
and are outside the embryonic area. Professor Mitrophanow,’ upon 
investigating the nature of these flecks, has arrived at some interest- 
ing conclusions regarding the origin of the egg-membranes of birds. 
According to the classical description of Foster and Balfour, the 
yellow of the egg is enclosed by a single “ vitelline ” membrane, the 
exact source of which, however, whether from the egg itself or from 
follicular cells surrounding it in the ovary, is unknown. 
Most recent investigators assign to it a follicular origin. Mitro- 
phanow finds that it is really a double membrane whose parts are of 
different origin. Its double nature is demonstrated by the occur- 
rence of the blood clots previously referred to not, as one might 
expect, on the outside of the vitelline membrane, or on its inner sur- 
face, but between the two laminz of which it is composed. 
Mitrophanow states reasons for believing that the blood clot can 
only have been deposited on the egg after it had left the follicle. If 
so, the outer lamina must have been formed in the upper part of the 
oviduct and accordingly must represent, not an ovarian product, but 
an accessory envelope. The delicate inner lamina Mitrophanow 
regards as a true vitelline membrane formed by the egg-cell itself. 
Origin of the Fauna of the Central African Lakes. —J. E. S. 
Moore has published ° very interesting researches on the fresh-water 
fauna of the African lakes, chiefly Lake Tanganyika. He divides 
the fauna into two constituents: (1) types which are represented 
generally in the African fresh-water bodies; (2) types which are 
found nowhere else in fresh water, but have relations in the ocean 
(halolimnic organisms). 
To the latter class belong the Medusz, discovered by Boehm in 
1883, numerous mollusks, both of the shore and of deeper water, and 
further two species of shrimps and a deep-water crab.’ 
The mollusks are allied, in many cases, not to a single marine form, 
1 Bibliographie Anatomique, Tome vi, Fasc. 2, pp. 69-84. 
2 Nature, vol. 58, 1898, p. 404 
3 These Crustaceans may prove to cited to the first class (generally distrib- 
uted fresh-water animals), since such forms, belonging to the shrimp genus 
Caridina and the crab family thssniaeiee are found all over the African con- 
tinent. — Rev. 
