PHYLOGENY OF THE PALiEOGNATH^E AND NEOGNATHCE. 259 



fundamentally from that of the Neognathce, since in these last it opens by a more 

 or less constricted aperture into the general cavity of the cloaca, whilst in the 

 Struthiones the exact opposite was the case, the cloaca opening into the bursa. 



" From this it will be at once evident that the cloaca does not open directly to 



the outer surface, but indirectly through the bursa by means of its large posterior and 

 inferior aperture." 



I find myself unable to confirm this point, and I think the accompanying figure will 

 justify me. The only difference which I can see between the Palceo- and Neognathce in 

 this particular is that in the latter the bursa opens into the roof of the proctodeum by 

 means of a minute aperture, in the former it opens by a very large one, so large as to 

 absorb nearly the whole roof of the proctodseum. 



"When these parts are dissected from spirit-specimens, in which hardening has taken 

 place in situ, Forbes's description seems to be amply verified, as I can testify. The 

 accompanying figure was made from a specimen in which the hinder end of the gut 

 had been removed soon after death, the cloacal aperture set widely open, and the 

 whole plunged into formol and left for two or three days. The wall of one side was 

 then removed and the true relations revealed. 



The function of the bursa is yet unknown. 



C. COPULATORT ORGANS. 



The Palceognathce all possess a well-developed copulatory organ. 



That of Struthio is a solid grooved organ containing erectile tissue and resembling 

 very nearly that of the Chelonia and Crocodilia. It can be retracted into a 

 pouch in the floor of the proctodeum. The m. protractor penis receives a slip from 

 the transversus analis, which descends from the pelvic bones. A pair of retractores 

 penis arise from the pelvis and are attached to the ventral aspect of the middle portion 

 of the organ. 



In the remaining Palceognathce the penis resembles that of the Anseres amongst 

 the Carinatce, being evertible and more or less markedly spirally twisted and grooved 

 dorsally. 



The copulatory muscles of the Palceognathce, Dr. Gadow [24] points out, differ 

 from those of the Neognathce, inasmuch as the latter are derived from the sphincter ani 

 solely, whilst in the Palceognathce they are partly differentiated from muscles which are 

 still attached to the pelvis, and are therefore skeleto-genital. 



DEVELOPMENT. 



The egg of the Palceognathce, save in Apteryx and perhaps the Crypturi, differs from 

 that of the Neognathce in that the pore-canals are branched. In Apteryx, as in the 

 Neognathce, they are unbranched. 



In Struthio, according to Nassonov [64], and Apteryx, according to Parker [71], an 



