120 
JOURNAL OF MAMMALOGY 
RECENT LITERATURE 
Bresslau, Ernst. The Mammary Apparatus op the Mammalia in the Light 
OF Ontogenesis and Phylogenesis. With a note by J. P. Hill. London: 
Methuen & Co. Pp. i-'vii, 1-145, with 47 illustrations. 1920. 
This splendid book is a resumd of the author’s extensive investigations on the 
development of the milk-glands and related structures in mammals and on the 
evolutionary history of the mammary apparatus. The subject is divided into 
three chapters describing the development of the mammary organs in the three 
principal groups of mammals, Monotremata, Marsupialia, and Placentalia. 
The development of the mammary apparatus does not begin with the arrange- 
ments for the accomodation of the young, i.e. with the formation of the pouch, 
but much earlier, with structures which the author terms primary-primordia, 
that is, gland areas. These are followed in Echidna by the development of the 
incubatorium and at last by mammary glands. The gland areas act as a hin- 
drance to the extension of the developing panniculus carnosus muscle immediately 
after birth. Thus there remains an oval, muscle-free area on the ventral side of 
the trunk which later develops into the incubatorium. In Ornithorhynchus the 
incubatorium is absent, most likely an adaptive feature in this aquatic animal. 
The marsupium or pouch in marsupials is in no way to be compared with the incu- 
batorium of Echidna. It arises as the result of developmental processes in the 
epidermis which lead to the formation of so-called marsupial pockets, which 
are entirely unrepresented in Echidna. The great apparent similarity of incuba- 
torium and marsupium in the adult animals rests solely on convergence. Among 
the Didelphyidse there are many pouchless forms in which a marsupium never 
existed. No pouch rudiments can be found in the Placentalia, since a pouch 
stage is not included in the phylogenesis of this group. 
The original nipple is represented by the simple type of eversion nipple which 
forms the common point of departure for the evolution of the marsupial as well 
as of the placental nipples. This type arises from the nipple pouches, discovered 
by Morgan, the final nipple appearing through eversion of the pouch. Another 
type, the so-called proliferation nipple, is formed through the involution of the 
nipple pouch stage. Here the nipple wall is formed essentially by the cutis, 
the apical portion only by the original primordia; whereas in the first mentioned 
type of nipple almost the entire epithelial covering is furnished by the original 
primordia. The so-called milk-streaks of placental embryos are homologous to 
the primary-primordia of monotremes and marsupials. From these milk-streaks 
spring the nipples and milk-glands of the Placentalia and their development is 
much like that in marsupials. 
The interesting discussions on the number and arrangement of nipples in 
marsupials, on the specializations of this organ in placentals, on the mammary 
hairs, and other related questions do not lend themselves for further condensa- 
tion in this review. It is to be regretted that some of the illustrations are not 
better reproduced. 
— A. H. Schultz. 
Michelsson, G. Die HautmusRulatur des Igels (Erinaceus europaeus). 
Morphol. Jahrb., vol. 51, pp. 147-229. 1921. 
A careful, detailed description of the cutaneous musculature of the hedgehog, 
Erinaceus europceus, and a comparison of these muscles with related structures in 
