COPULATORY ORGANS OP THE AMNIOTA. 
31 
portion of the cloaca. It is found in Urodela only, e.g. in Salamandrina per spirilla t-a 
and in Triton platycephalus. In the latter it consists of an erectile cone, which 
Wiedersheim considers as derived from the caudal portion of the cloacal lips. This 
dorsal unpaired, median, still very rudimentary organ, is a type restricted to Amphibia. 
Another type of low standing is met with in the Gymnophiona and to a less pro¬ 
nounced degree in Hatteria. The immissio seminis is secured by the finger-of-a-glove- 
like eversion of the cloacal walls, chiefly of those of the proctodseum. This type is 
best developed in the Gymnophiona. In them a great portion of the cloaca can 
through its strong muscular coating be converted into a tube projecting several centi¬ 
metres, and is then used as an intromittent organ. A bifurcated M. retractor, which 
arises from the abdominal walls, is attached to the recessus of the middle portion of 
the cloaca. In the female the cloaca is short and cannot be protruded (cf Wieders¬ 
heim, £ Anatomie der Gymnophionen,’ figs. 88 and 89, Taf. ix.). 
From this stage, which probably represents that of the Proreptilia and of the true 
Reptiles before their separation into Crocodilia and Chelonia and into Sauria and 
Ophidia had taken place, we can, I think, derive the types of the other Amniota. 
The definition that the copulatory organs of the Lizards and Snakes are connected 
with the posterior or dorsal, but those of the other Amniota with the anterior or 
ventral wall of the cloaca, seems to ha.ve led to the misconception that no homology 
can be traced between these two types of penes. 
To clear this question up, I draw attention to the following considerations:— 
1. In Hatteria and in the Gymnojdriona, as explained above, the inner walls of the 
cloaca form by protrusion and evagination a temporary intromittent organ. 
2. In the embryos of Lizards the anus is still round, and not a transverse slit. On 
each side, the lateral inner walls of the proctodeeum are, together with part of the 
uro-anal fold F, raised up into prominent cones, which afterwards are invaginated and 
withdrawn into the post-anal region of the tail by the action of specialised muscles. 
In connexion with this the anal opening assumes its typical transverse shape. 
In the Snakes, which are the most specialised branch of the Saurian stock, the 
original position of the penes is coenogenetically obscured, although still traceable. 
3. The original duplicity of the “ unpaired ” copulatory organ of the other Amniota 
is still indicated by the nerve supply, the vascular supply, by the corpora cavernosa 
5. crura penis, by the double penis and clitoris of certain Marsupials, like Didelphys, 
and by the fact that in the Chelonia the peritoneal canals are continued far into the 
lateral portions of the penis. 
4. The completely divided right and left penes of the Lizards and Snakes are 
supplied by the same nerves as are the copulatory organs in all the other Sauropida. 
These circuinstances, considering also the modifications of the cloaca as described in 
this paper, seem to me to permit the following conclusions :— 
That in all Amniota the intromittent organs, no matter if double or single, are 
derived from the walls of the outermost cloacal chamber, in connexion with the 
