When the embryos are at this stage their number may be estimated in the following manner: The whole mass of embryos is carefully scraped from the beard of the mother oyster by means of a small hair brush. The whole mass is then weighed, and afterward a small portion of the mass. This small portion is then diluted with water or spirits of wine, and the embryos portioned out into a number of small glass dishes, so that they can be placed under the microscope and counted. Thus, knowing the weight of the small portion and the number of embryos in it by count, we can estimate the total number of embryos from the weight of the entire mass, which is also known. In this manner I estimated the number of embryos in each of five full grown Schleswig-Holstein oysters caught in August, 1869, and found that the average number was 1,012,956. Notwithstanding this great fecundity, but an extremely small proportion of the young oysters produced during the course of the summer arrive at maturity, 421 only out of 500,000,000 escaping destruction. The immolation of a vast number of young germs is the means by which nature secures to a few germs the certainty of arriving at maturity. In order to render the ideas of germ-fecundity and productiveness more easily understood, Prof. Mobius makes the following comparison between the oyster and man: According to Wappaus, for every 1,000 men there are 347 births. According to Bockh, out of every 1,000 men born 554 arrive at maturity, that is, live to be twenty years or more of age; thus, on an average, 347 children are produced from 554 mature men, or 626 children from 1,000 mature men. Since 1,000 full-grown oysters produce 440,000,000 of germs, then the germ fecundity of the oyster is to the germ fecundity of man as 440,000,000 to 6.26, or as 7,028,754 to 1. On the other hand, the number which arrive at maturity is 579,002 times as great with mankind as with the oyster; for of 1,000 human embryos brought into the world 554 arrive at maturity, or of 440,000,000 newly born 243,760,000 would live to grow up, while of 440,000,000 young oysters only 421 ever become capable of propagating their species. The proportion is then 421 to 243,760,000, or as 1 to 579,002. I am fully persuaded that these figures represent the number of oysters which arrive at maturity more favorably than is really the case, since from every thousand of full grown oysters it is certain that, on an average, more than 440,000,000 young are produced. * * * * * RED SKY. The beautiful red sky which has been so frequent of late, morning as well as evening, has excited much comment. The comment, however, has consisted more of description, statement of fact, theory, and wonder as to cause, rather than as to satisfactory explanation.