was caught was not quite as large as the female, either in length or circumference, and altogether a more slim fish. I think we may reasonably expect to receive the specimens by the first of December. But I can hardly hope to get satisfactory specimens of the fish as I found it, with young well grown, before the return of the same season, viz., June. By that time I trust the facts will be fully decided, and the results, as important as they may be, fully appreciated." Dr. Jackson's specimens came from Sausalito Bay, near San Francisco. Soon after the publication of this letter a similar discovery was made independently by Dr. William P. Gibbons, of Alameda. Still other specimens were made known in 1854 by Dr. Charles Girard, these having been collected in connection with the United States Pacific Railroad Surveys. The species first examined by Dr. Jackson was named by Agassiz _Embiotoca jacksoni_. In Professor Agassiz's comments on Dr. Jackson's discovery he makes the following observations (_Amer. Jour. Science and Arts_, 1854): "The female genital apparatus in the state of pregnancy consists of a large bag the appearance of which in the living animal has been described by Mr. Jackson. Upon the surface of it large vascular ramifications are seen, and it is subdivided internally into a number of distinct pouches, opening by wide slits into the lower part of the sac. This sac seems to be nothing but the widened lower end of the ovary, and the pouches within it to be formed by the folds of the ovary itself. In each of these pouches a young is wrapped up as in a sheet, and all are packed in the most economical manner as far as saving space is concerned, some having their head turned forwards and others backwards. _This is, therefore, a normal ovarian gestation._ The external genital opening is situated behind the anus, upon the summit and in the center of a conical protuberance formed by a powerful sphincter, kept in its place by two strong transverse muscles attached to the abdominal walls. The number of young contained in this sac seems to vary. Mr. Jackson counted nineteen; I have seen only eight or nine in the specimens sent by Mr. Cary, but since these were open when received it is possible that some had been taken out. However, their size is most remarkable in proportion to the mother. In a specimen of _Emb. jacksoni_ 10½ inches long and 4½ high the young were nearly 3 inches long and 1 inch high; and in an _Emb. caryi_ 8 inches long and 3¼ high the young were 2¾ inches long and ⅞ of an inch high. Judging from their size, I suspected for some time that the young could move in and out of this sac like young opossums, but on carefully examining the position of the young in the pouches, and also the contracted condition of the sphincter at the external orifice of the sexual organs, I remained satisfied that this could not be the case, and that the young which Mr. Jackson found so