BULLETIN OF THE UNITED STATES PISH COMMISSION. 137 



(Solley, 3; Owen; Cooper; Hunter, 1; Geoffrey St. Hilaire; Eapp; Eu- 

 dolphi ; Turner). It is therefore likely that the anterior and posterior 

 acini would be developed most rapidly and become longest, and not pre- 

 sent nearly so uniform a length and such a pronounced radiated arrange- 

 ment as in most other Mammalia, in which the gland is discoidal and 

 more or less conical, but resemble to some extent, at one stage of develop- 

 ment, the unspccialized condition of the organ seen in Echidna. 



But the preceding may perhaps be considered pure speculation, and 

 possibly quite out of the way so far as it is intended to describe the 

 mode in which the adult gland is formed. The latter has long ago, as 

 described by Hunter, Cooper, and St. Hilaire, a large ampulla or lac- 

 teal sinus, which traverses its center longitudinally along its middle. 

 The involuted rudiment which I have figured may send out two great 

 processes from its enlarged end, an anterior and a posterior one, from 

 the sides of which the secondary acini of the adult gland may bud out 

 laterally on either side. This is the more probable mode of develop- 

 ment, for we find that the subsidiary lateral ducts open at intervals into 

 the median lacteal sinus, along the sides of the latter, in the adult organ. 



The coarse anatomy of the adult mammary gland of Phoecena is pretty 

 well known, and it will therefore be superfluous to enter into a very de- 

 tailed account of the organ. It is a flat glandular mass nearly 3 

 inches wide, somewhat over a half inch thick in its center or in the re- 

 gion of the nipple, and nearly or quite a foot in length. Externally or 

 ventrally it is invested by connective tissue, and overlaid first by what 

 are apparently dermal muscles and then by the tough, fibrous, skin which 

 is not underlaid by blubber here or in the vicinity of the vulva. The 

 nipple opens from the mammary sinus and is placed below the hinder 

 half of the gland. As in Balamoptera (Turner, 12), there is a single 

 opening in the nipple, the numerous orifices in it described by Owen 

 being apparently the pedunculate bodies at its tip figured by Turner, 

 and, as surmised by Gegenbaur (6), do not indicate the existence of 

 numerous milk ducts opening on its apex. 



The apex of the nipple in Phoecena, unlike that of Balcenoptera, is quite 

 smooth, somewhat flattened laterally by compression between the folds of 

 the external mammary fossa, and shows a very distinct single terminal 

 opening in its center, which is continuous by way of a single canal with 

 the wide mammary sinus below. 



From the description given by Turner of the enormous mammary 

 gland of a gravid specimen of Balamoptera, the inference may be drawn 

 that there is but little difference between the structure of the mammary 

 organs of the Denticete and the Mysticete. 



In both there seems to be good reason for believing, with the editor 

 of the posthumous edition of Hunter's paper (1), that the milk accumu- 

 lates in the great mammary sinus and is rapidly forced out by the vo- 

 lition of the mother, by compression through the action of the overlying 



