10 MH. P. H. A. MARSHALL ON [Jan. 14, 



specimens of Parastacus he saw as follows : — " H y a sur le coxo- 

 podite de la troisi^me jambe, une ouverture ovale qui est fermee 

 par un ecusson bomb6 et que Ton peut deprimer du cote median 

 ou libre." The state of preservation was not good, but von Ihering 

 says : — " II m'a paru qu'un conduit tres delicat se dirigeait plus en 

 avant, a I'ouverture du troisieme coxopodite, raais je ne puis 

 I'aiSrmer." Whether or not the specimens dissected were her- 

 maphrodite, von Ihering is apparently also doubtful. 



Faxon records the coexistence of both pairs of apertures in all 

 the specimens he has examined of Parastacids saffordi, P. vari- 

 cosus, P. defossis, and P. hassleri, but not in specimens of 

 P. agassizii. l^o account of the internal genital organs is given 

 by Faxon. 



The best and most recent account of the supernumerary aper- 

 tures and ducts of Parastacus is by Lbnnberg, who describes both 

 sexes, which differ not only in their internal but also in their 

 external characters. The species described is P. hassleri. Not 

 only do the males have supernumerary apertures and ducts in 

 the 11th somite, but the females also in the 13th somite, in the 

 position of the normal apertures of male crayfish. Although the 

 supernumerary ducts have a lumen they are not functional, since 

 the additional genital orifices in the male are only shallow grooves 

 and those in the female are closed by a membrane. The additional 

 openings in the male are closely similar in appearance to the 

 functional openings of the female. Lonnberg states that he has 

 found bodies resembling eggs in the testis, but he thinks it im- 

 probable that they " can be fully developed, still less of propagative 

 u.se." He draws the conclusion that " in Parastacus hassleri a 

 partial hermaphroditism is prevailing." It is interesting to note 

 that the apertures in most species of Parastacus ^ are on the same 

 somites as in the abnormal Astacus described by Benham. 



In view of the freqvient occurrence of genital apertures in 

 Nephrons on the basal joints of other legs than the third and 

 fifth, the coexistence of apertures upon these legs cannot be 

 I'egarded as conclusive evidence of a partially hermaphrodite 

 condition as some authors have supposed. Apertures on the 

 fourth pair of legs have not, so far as I know, been I'ecorded for 

 Parastacus, but it is not unreasonable to suppose that if a large 

 number of specimens were examined they would be found to 

 occasionally occur. 



To those who will regard the abnormal genital openings in 

 Nephrops as evidence that the apertures and ducts were meta- 

 merically repeated in past times, all the above-cited cases must be 

 interesting in view of Lankester's suggestion that the genital 

 ducts of Arthropods are derived from nephridia. Allen has 

 described the genital ducts in young adults of Paloimonetes as 



1 Mr. Borradaile has called my attention to the fact that in male specimens of 

 Faffurus deformis M.-Edw. the female apertures also normally occur. Vide Borra- 

 daile, " On some Crustaceans from the South Pacific, Part II.," P. Z. S. 1898, where 

 references are given. 



