404 



WHITMAN. [Vol. IV. 



months of November, December, and January, The male seizes the 

 female with his large nippers, turns her over, and whilst he holds her 

 lying on her back, places himself in such a manner as to pour out the 

 fecundating material upon the two outer lamellae of the tail. After this 

 first operation, which lasts some minutes, he conveys her rapidly beneath 

 his pleon, in order to effect a second deposition of semen upon the 

 plastron round the external opening of the oviducts, by means of the 

 curious mechanism so accurately described by M. Coste, upon the plates 

 of the caudal fan. {Ripisura.) 



" According to the degree of the maturity of the ova at the time of 

 the union of the sexes, oviposition takes place at a period varying from 

 ten to forty-five days after copulation. . . . Immediately after ovi- 

 position (which usually takes place during the night, and is accompanied 

 with an emission of mucus for securing the eggs) we may detect in this 

 mucus and water the presence of spermatozoids, precisely similar to 

 those which are contained in the spermatophores attached to the 

 plastron, and derived from them." 



These spermatophores still remain attached to the plastron 

 long after oviposition. 



" They consist of small white coriaceous filaments, either isolated or 

 mutually adherent ; they no longer show anything but a central cavity, 

 in which the microscope reveals only a few more or less withered sper- 

 matozoids. The wall of these spermatophores retains its thickness, and 

 remains, as before, composed of a concrete, striated, tenacious mucus." ^ 



Fecundation [p. 230] is thus accomplished after oviposition. This 

 is concluded from the fact that spermatozoa are found in the mucus 

 surrounding the eggs, and from the fact that the spermatophores are 

 then empty.^ 



POSTSCRIPT. 



Dr. C. T. Hudson, who has recently given us the results of 

 observations continued for upv^ards of thirty years on the Ro- 

 tifera, seems to doubt Plate's statements regarding the injec- 

 tion of spermatozoa through the body-wall. In his presidential 



1 Comptes Rendus, Jan. 15, 1872, LXXIV, pp. 201-2 ; Ann. Nat. Hist., 4th Ser., 

 IX, pp. 173-74. 



2 Cf. A. Lereboullet: Recherches d'' Embryologie compar'ee sur le Developpement 

 du Brocket, de la Perche et de VEcrevise. Paris, 1 862. p. 652. 



