68 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XIV. 



sinus and is a highly developed organ, deeply bifid, and attached only 

 at its base. It consists of two long, smooth, and sharply pointed rods 

 the apices of which reach nearly or quite to the cloacal opening of the 

 urogenital sinus. Each of these divisions is sharply and deeply grooved 

 on the dorsal surface of its basal half. The entire organ is 3.5 mm. in 

 length and of this each fork is 3 mm. The form of the clitoris, therefore, 

 is not very unlike that of the divided glans penis of the male. In an old 

 female, the clitoris appears to be a single organ, hanging free, and having 

 several longitudinal plications and a transverse cleft behind its rather 

 blunt apex. 



The cloaca is inclosed in an extensive muscle, the sphincter cloacae. 

 It surrounds the cloacal orifice and spreads over the large rectal glands, 

 terminating anteriorly in a transverse plexus of nerves and muscle 

 fibers which is attached to the ventral surface of the urogenital sinus 

 and which sends fibers and fascia into the pelvic cavity. The relations 

 of the rectal glands have been described elsewhere (p. 76). 



From 'the comparative standpoint, the female reproductive organs 

 of Canolestes are more significant than those of the male. They are 

 distinctly of a diprotodont rather than a polyprotodont type. This is 

 evidenced at once by the deep median vaginae and the long lateral vag- 

 inal canals. Many polyprotodonts give birth to their young by way of 

 the lateral vaginae. In fact this seems th3 only method possible in such 

 forms as Didelphis which have extremely small median vaginae. Cer- 

 tain others do not conform to this rule, as Perameles, which Hill (1899) 

 has shown to have a parturition somewhat less perfected but similar to 

 that of the Macropodidae, in which the foetus has direct passage from 

 the median vaginae to the urogenital sinus and thence to the exterior. 

 In certain other respects the reproductive system of Perameles is re- 

 garded by Hill as primitive. Data are not available as to the phenomena 

 of parturition in all diprotodonts, but the direct median passage has 

 been observed, according to Fletcher (fide Hill, 1899, p. 74), in no less 

 than twelve species of Macropodidae. Hill found it also in Tarsipes, and, 

 although it is evident that much study of well prepared serial sections is 

 necessary for a thorough understanding of the subject, the inference is 

 very strong that those forms having large median vaginae and relatively 

 long convoluted lateral canals give birth to the young by median 

 rather than lateral passage, some by an opening from the median vaginae 

 to the urogenital sinus which becomes permanent after the first parturi- 

 tion, and others by a rupture at this point and subsequent closing for 

 each parturition, the connection being made through a "pseudo-vaginal 

 canal" in the connective tissue. This method of parturition is at least 

 functionally an approach to the method in the higher mammals having 



