. The physiology of reproduction. Reproduction. 244 THE PHYSIOLOGY OF REPRODUCTION When the venous spaces in the erectile tissue are distended with blood the organ erects, becoming hard and rigid in con- dition. It is this power of erection which enables the penis to function as an intromittent organ during copulation. The above description applies more especially to the copulatory organ in Man. In the other groups of Mammals it has essentially the same structure, but presents sundry modifications in the different orders.^ In the Monotremata,. Fig. 59.—Section through erectile tissue. (After C
. The physiology of reproduction. Reproduction. 244 THE PHYSIOLOGY OF REPRODUCTION When the venous spaces in the erectile tissue are distended with blood the organ erects, becoming hard and rigid in con- dition. It is this power of erection which enables the penis to function as an intromittent organ during copulation. The above description applies more especially to the copulatory organ in Man. In the other groups of Mammals it has essentially the same structure, but presents sundry modifications in the different orders.^ In the Monotremata,. Fig. 59.—Section through erectile tissue. (After Cadiat, from Sohafer.) a, trabeculEB ; 6, Yenous spaces ; c, muscular fibres cut across. however, there is no corpus spongiosum.^ In some Mammals (Carnivora and Rodentia) the penis is provided with a ' For an account of the structure of the copulatory organ in the various groups of Vertebrates, with notes on the diiferent modes of copulation and bibliography, see Gerhardt, " Morphologische und biologische Studien iiber die Kopulationsorgane der Saugethiere," Jenaische Zeitschr. f. Naturwissen- scha/t, vol. xxxix., 1905. ^ The penis of the Monotreme is perforated by a canal, through which the semen passes but not the urine. When in a relaxed state the organ lies in a little pouch in the floor of the cloaca, from which it projects when erected. The cloaca is the single common chamber through which the fieces and urine pass to the exterior, as in birds and reptiles. In birds the penis is either altogether absent or else is rudimentary {Crax, Crypturus, Lamel- lirostres, Katltse), Disselhorst, " Gewichts- undVolumszunahmedermannlichen Keimdriisen," &c., Zool. Anz., vol. xxxii., Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Marshall, F. H. A. (Francis Hugh Adam), 1878-1949; Crame
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