WAGENER^ ON GYRODACTYLUS ELEGANS. 307 



and during the formation of the embryo it disappears alto- 

 gether. 



To the sexual system must also be referred a peculiar penis- 

 like organ which has not been noticed by v. Siebold. 



It is placed close behind the pharynx, beneath the integu- 

 ment on the upper boundary of the intestinal tube ; and con- 

 sists of a sacculus inclosing the proper penis, and having 

 attached to it three peculiar sacciform organs. 



The penis-sac is of a pyriform shape, or almost spherical ; 

 and it appears to be perforated at the obtuse point by which it 

 is in contact with the integument, and this orifice is sur- 

 rounded in a radial manner with from eight to sixteen hooks, 

 the uppermost of which is distinguished by its size and figure. 

 The points of all the hooks are directed towards the common 

 centre, the apparent orifice of the sac; their bases are en- 

 larged and spoon-shaped, the broad surface being applied upon 

 the wall of the sac ; and from either side of the base of each 

 hook a streak proceeds in a meridian direction upon and im- 

 mediately beneath the surface of the sacculus. 



The large hook appears to have two lateral processes, 

 by which it is affixed upon the obtuse angle of a triangular 

 basal portion. 



On the bottom of this armed sacculus lies a minute 

 pyriform body, perforated in its longitudinal axis, and occu- 

 pying about a quarter of the sacculus, with which the middle, 

 sacciform organ, which is distinguished by a thick membrane 

 and opaque granular contents, appears to be immediately 

 connected. The sacculus is somewhat convoluted, and pre- 

 sents a constriction such as may usually be observed in the 

 vesicula seminalis externa of the Distomata. 



I never noticed spermatozoa in it, nor could any channel 

 be traced between it and the testis. On either side of this 

 sacculus, which may be compared to a rudimentary vesicula 

 seminalis, are placed two double follicles or sacs. 



The two upper are elongated, and smaller than the two 

 lower spherical ones. Their contents consist of a fine gra- 

 nular matter, and each division presents a clear nucleus, 

 and opaque nucleolus. These organs cannot be compared to 

 the vesicles connected with the penis of Dactylogyrus fallax, 

 which are fitted with a viscous brown material, and situated 

 on either side of the seminal vesicle. 1 



The ovum of Gyrodactylus elegans, after its detachment 

 (an act which it may be remarked has not yet been observed, 

 owing, as it would seem, to the great slowness with which 

 it takes place), is a transparent globule or cell with anucleus, 

 as clear as water, and sharply defined, though the nucleolus, 



