134 Proceedings of Scientific Societies. 



PROCEEDINGS OF SCIENTIFIC S0CIE7IES. 



SAN FRANCISCO MICROSCOPICAL SOCIETY. 

 December 17TH, 1S90. 



The regular "meeting was held at its rooms, 130 Sutter street, 

 -with President Wickson in the chair. Besides a good attendance 

 of members, a number of visitors was present. 



After the usual routine business had been transacted, the 

 President announced that the lecture of the evening would be by 

 C. H. Eigenmann, Ph. D., on ''The Embryology of Viviparous 

 Fishes." 



The speaker began by informing his hearers that the waters of 

 the California Coast abounded in viviparous fishes, the perch 

 and the rock cod being well-known representatives of that class. 

 His investigations had been confined to fishes near the shore, 

 where the depth did not exceed one hundred fathoms; but the 

 deep-sea species examined by the naturalists of the Albatross 

 showed the same preponderance; of the viviparous class. 



The specimens of fishes shown last night were the common 

 "shiner" of our bay, the Micrometrus aggregatus of scientists . 

 Every stage of development was shown, either by careful pre- 

 pared and stained sections of the embryo, or by dissections of 

 the matured forms. The eggs of Micrometrus are the smallest 

 fish ova yet described, measuring only a little over one one-hun- 

 dred-and-fortieth of an inch, or less than those of most mamalia. 

 The average pelegic fish egg has a diameter of one milimeter, or 

 one-thirty-second of an inch, only a very minute portion of which 

 segments and takes part in the formation of the embryo. The 

 egg is deposited by the mother in the water, where it lies or 

 swims unprotected. As the tail of the young fish is formed it 

 begins to move, first feebly and then vigorously, until the mem- 

 brane surrounding the egg is burst and the young fish swims out. 



The development of Micrometrus differs from the usual mode 

 in some very essential particulars, as this form belongs to a fam- 

 ily of viivparous fishes almost exclusively confined to the west 

 coast of North America. All the members of this family give 

 birth to their young in an advanced stage. At the time the eggs 

 are npe the ovary is no thicker than a goose-quill, and the ovifer- 

 ous tissues are folded upon themselves. With the growth of the 

 embryos the walls of the ovary become greatly distended, the 

 oviferous sheets unfolding at the same time. In Micrometrus 

 the active period begins when the eggs are ripe, and culminates 

 at the time the young are set free. In other words, the eggs be- 

 come ripe when in ordinary fishes they only begin their most 

 active growth. 



Dr. Eigenmann illustrated his lecture with drawings at the 

 black-board, and also by very carefully made drawings in India 

 ink. The latter were made with the camera lucida, and conse- 

 quently were all drawn, to scale. The speaker's remarks were 

 received with marked satisfaction by those present, and he 



