BULLETIN OF THE UNITED STATES FISH COMMISSION. 14 1 



the epidermis of the embryo, which is covered internally by the stratum 

 Malpighii, as in other mammals. 



2. The acini of the gland probably develop in the same way as in the 

 same organ in other mammals, except that the gland begins to elongate 

 very early and develop a great longitudinal median sinus in its middle 

 portion, which is directly continuous with the dnct which opens through 

 the nipple. 



3. The folds which surround the nipple fossa and inclose the nipple 

 arise very early, as shown by the condition of the gland in two succes- 

 sive stages represented by an embryo of Globiocephahis 2 inches long 

 and one of Rhachianectes 5J inches in length. 



4. The gland as found in Cetacea, while displaying peculiar teleologi- 

 cal modifications, must, so far as the mature anatomy and early devel- 

 opment of the organ is concerned, be included with the type defined by 

 Gegenbaur as possessing pseudo nipples. 



5. The sexes of Cetacean embryos, judging from those of Olobioceph- 

 alus and Phocwna may be discriminated from each other externally 

 when somewhat under 2 inches in length, by the differentiation of the 

 external genitalia.* 



In conclusion I would express my appreciation of the kindness of 

 the curator of the Department of Mammalia in often, finding for me, I 

 fear, at considerable trouble to himself, the materials, in the way of 

 specimens and literature in the Museum collection, upon which this in- 

 vestigation is based. 



BIBLIOGRAPHY. 



1. J. Hunter. Observations on the structure and ceconomy of whales. 



Philos. Trans., lxxvii, 1787, pp. 371-450. 



[The copy consulted by me was an annotated posthumous edition ; editor 

 not known ; title page wanting.] 



2. T. S. Traill. On the structure and uses of the mammary glands of 



the Cetacea. Edinb. New. Philos. Journ., xvii, 1834, pp. 363- 

 364. 



3. S. Solley. Article " Mammary gland," Cyclop. Anat. and Physiol., 



iii, p. 252. 



4. C. Langer. Ueber den Bau und d. Entwickeluug der Milchdrfisen. 



Denkschrifteu d. k. Akad. d. Wiss. Wien, iii, 1851. 



5. M. Huss. Beitr. zur Eutwick. d. Milchdrfisen b. Menschen und Wie- 



derkauern. Jenaische Zeitschr., iii, 1873. 



" I have not been able to find any papers dealing with the development of the mam- 

 mary "lauds of Cetacea, though a thorough search of the literature may reveal the 

 fact that such investigations have been previously made. The results which I have 

 obtained have seemed to me of sufficient interest to warrant their publication, aiding 

 as they may in giving us some additional light in a departmeut of vertebrate em- 

 bryology in which it is very difficult to obtain foetuses young enough for the prose- 

 cution of such studies. 



