MR J. D. MACDONALD ON THE ANATOMY OF THE GENUS FIROLA. 191 



of the neck, directly near the arms ; but as Rang (Mem., loc. cit., p. 878, PI. ix. : 

 or Isis, 1832, Taf. vii.) has found this penis with all the individuals he has 

 examined, it may be questioned if the sexes are really separate with this 

 Heteropod. 



" The internal genital organs of Atlanta and Phpllin'hoe, should be thoroughly 

 studied for the elucidation of this point." 



There are a good many references made in this note, but no satisfactory infor- 

 mation is derived from any of them. The paucity of female Atlanta?, as indicated 

 by M. Rang having only encountered the males, is perhaps the most interesting 

 point. This was for a long time my own experience also, but on several occasions 

 I have been fortunate enough to obtain indisputable females. 



Though the position of PhylUrrho'e amongst the Nudibranchs and not with the 

 Heteropods, has been long recognised by zoologists, I may make the following 

 remarks in passing, to clear up a desideratum in the note. First of all, the bifid 

 penis of this mollusc is perfectly retractile, and its testicular follicles are included 

 within the saccule of the ovaria, so as to form perfect hermaphrodite glands. The 

 primary vas deferens and oviduct are blended together ; and subsequently to the 

 formation of stout fusiform spermatheca, the common tube divides into outer ovi- 

 duct and outer vas deferens, the one passing into a wide glandular uterus, and the 

 other into one of the limbs of the intromittent organ. The bisexual nature of the 

 animal was known to Cuvier, though he could not have given this interpretation 

 of it. 



Having examined some hundreds of recent Heteropoda, particularly the species 

 oi Atlanta, it struck me as being very odd, that I had never in a single instance 

 succeeded in tracing a vas deferens onwards to the external male organ. This finally 

 led me to believe that the penis was imperforate, and as in Onchidium, Aplysia, 

 Melo, and numerous other Gasteropoda, far in advance of the spermatic opening, 

 both being held in communication by a ciliated groove, more or less capable of 

 being converted into a canal. Of the truth of this doctrine, 1 am now fully con- 

 vinced, for the outlet of the spermatic duct, as given in the figure, and which is 

 even quite prominent in Firoloides, is so palpable as to admit of no question ; and 

 on closely examining the duplex penis, I find by the simple test of focussing, 

 that the so-called perforation and internal canal are nothing more than an 

 external, deeply-grooved, and ciliated tract, the office of which is obvious enough. 



