ON THE ARRANGEMENT OF THE FCETAL MEMBRANES IN THE CETACEA. 503 



was very great, and the capillary network was distributed not only within the 

 villi, but beneath the intermediate portions of the membrane. Hence; two 

 extensively diffused highly vascular surfaces, a maternal and a foetal, were 

 brought into close apposition with each other, and it is to this arrangement, 

 I believe, that we are to look for the structures concerned in placental 

 respiration. 



The conditions, however, under which the interchange of gases takes place, 

 differ very materially in the pulmonic and placental respiratory organs. In 

 the lungs the gases dissolved in the blood have to be interchanged with the 

 air in the air-cells. In the placenta the gases are in a state of solution on the one 

 side, in the foetal, on the other, in the maternal blood, and the transmission of 

 the dissolved gases would take place through the thin layer of fluid secreted by 

 the utricular glands, which bathes the surface of the chorion. The physical 

 conditions approach therefore more closely to what we find in aquatic rather 

 than in ordinary atmospheric respiration. 



EXPLANATION OF PLATES. 



Figures I, 2, 7, 13, and 16, were drawn from nature, under my superintendence, by Mr J. B. 

 Abercrombie; figures 10, 11, 12, 14, and 15, by Millen Coughtrey, M.B.; and figures 

 3, 4, 5, 6, 8, and 9, by myself. 



Plate XVII. 



Figure 1. Gravid uterus of Orca gladiator, witb tbe cavities opened into, reduced f^th. The single 

 arrow is passed through the corpus uteri from one cornu to the other. The double- 

 headed arrow is passed into the canal of the cervix ; a, the ovary ; b b, the Fallopian 

 tubes, of which the right is cut through ; c c, the round ligaments ; d, the bladder with 

 the urethra leading from it ; e, the mouth of the vagina. 



Figure 2. A vertical section through the ovary reduced one-half, a, the large corpus luteum with its 

 central cicatrix ; b, the highly vascular body at the hilum. 



Figure 3. Cells of the corpus luteum. x 320. 



Figure 4. A magnified vertical section through the uterine mucous membrane, a, crypt layer ; b, 

 glandular layer ; c, transversely divided gland-tubes beneath the crypt-layer ; d, a funnel- 

 shaped crypt with a gland opening into it, the free ends, and not the sides of the 

 cylindrical epithelium of the glands, were seen in this specimen ; e, a cup-shaped crypt ; 

 g, sub-epithelial corpuscles of the crypt. 



Figure 5. A magnified view of the utricular glands, with the intermediate connective tissue, as seen in 

 a horizontal section through the glandular layer of the mucous membrane. 



Figure 6. A highly magnified view of an uninjected compound villus of the chorion. The secondary 

 club-shaped villi are shown with the corpuscles of their connective tissue. The sub- 

 epithelial corpuscles are indicated at a. 



Figure 7. A view of the allantois and amnion displayed by everting these membranes, reduced T Vth ; 

 a, the funis ; b b, the horns of the allantois ; c c, the horns of the amnion ; d, the 

 amniotic corpuscles, of which d' represents the corpuscle situated near the tip of the left 

 horn of the amnion. 



Figure 8. Cell structures from an amniotic corpuscle. x 480 diameters. 



VOL. XXVI. PAKT II. 6 P 



