346 PEOPESSOR RAY LANKESTER AND A. G. BOURNE. 



It is curious that this aperture has been overlooked by every 

 student of the Nautilus excepting Keferstein. At the same time 

 Keferstein failed to apprehend its true significance. 



Keferstein showed that the aperture (/. ov.) leads by a duct 

 into the " pyriform appendage/^ originally described by Owen 

 as lying iu close connection with the ventricle of the heart. 

 The nature of this pyriform appendage neitlier Owen nor any 

 subsequent observer was able to divine. Keferstein first 

 showed that it communicates with the exterior by means of the 

 aperture (/. ov.), discovered by him. 



But this aperture is the exact left-hand representative of the 

 large oviducal aperture (r. ov.). This suggested to us the inquiry 

 as to whether the relations of the " pyriform appendage " 

 are such as to favour the supposition that it is a rudimentary 

 left oviduct. We find that they are; and we conclude that 

 in Nautilus the left oviduct is reduced to a rudimentary condi- 

 tion, becomes constricted at the point where it joins the ovary, 

 and so ends blindly as " the pyriform appendage," whilst still 

 opening to the exterior by the left genital pore (I. ov.). The re- 

 lation of the right and left oviducts to the ovary, to the ven- 

 tricle of the heart, and to one another, is shown in the diagram 

 (fig. 4.) Whether the ovary is a medium structure, or whether, 

 on the other hand, the pyriform appendage represents an 

 aborted ovary, as well as a rudimentary blindly ending oviduct, 

 is a matter for further inquiry. 



Our conclusion as to the nature of the aperture {I. ov.), and 

 the pyriform appendage of the female, was greatly strengthened 

 by our discovery of a precisely similar disposition of parts in the 

 male. 



The same number of apertures is present in the male 

 Nautilus (fig. 2) as in the female. Instead of the right ovi- 

 duct with plaited mouth, we have a right sperm-duct produced 

 into a large penis-like structure (pe.). The aperture marked 

 /. sp. in fig. 2 has not hitherto been noticed, nor has the pyri- 

 form appendage been observed hitherto in a male Nautilus. 

 We find that, just as in the female, the left aperture (I. sp.) 

 leads into a " pyriform appendage," which ends blindly. As 



