WAGENERj ON GYRODACTYLUS ELEGANS. 



197 



which the " daughter " individual is developed a " germ- 

 cell/^ and sought the terminal member of the series of gene- 

 rations among the Polystomata. 



In the following observations the sexual reproduction of 

 Gyrodactylus elegans will be proved^ and^ at the same time, 

 some of the points in its organization, as described by 

 Von Siebold, will be more fully elucidated. 



Habitation. — Gyrodactylus elegans is found on the gills of 

 all the Cyprinoid fishes brought to the Berlin market ; it 

 also occurs on the fins and abdominal surface of the fish, and 

 may be obtained by scraping off the slime. Up to the 

 present time, it has been found in the following species of 

 fish: 



EsoiV lucius 

 Cyprinus Carpio 

 Gobio 



)) 



y> 



i> 



}> 



Brama . . 

 carassius 

 phoxinus . . 

 erythrophthalmus 

 „ alburnus . . 

 Cobitis fossilis . . . 

 „ barbatula . . 

 Gasterosteas aculeatus 

 ,, IcBvis 



The Pike. 

 Carp, 

 Gudgeon. 

 Bream. 



Prussian Carp. 

 Minnow. 



Budd, or Red Eye. 

 Bleak. 



Pond Loach. 

 Loach. 

 Stickleback. 





And from a drawing kindly furnished to me by Dr. Semper, 

 a species very similar to, if not identical Avith, G. elegans, 

 appears to occur on the gills of Cyclopterus Lumpus (Lump- 

 Sucker). 



Presuming that Nordmann^s figure is correct, specific 

 distinctions would seem to exist between the hooks of the 

 species noticed by him and that which has formed the subject 

 of my observations ; but I have reason to believe that these 

 difi"erences arise merely from trivial inaccuracies which it is 

 very difiicult to avoid making in the representation of the 

 hooks. 



Size. — The largest individual observed by me was about 

 ■i- mm. = T-i-o inch in length, and its greatest breadth might 



be about -|- mm. 



= -T^ inch. 



Form. — The form of the animal is flattened and tongue- 

 shaped, with rounded borders. The cephalic extremity 

 is divided into two short, slightly ventricose lobes, and is 

 about -tV mm. = -^^ inch in width. To the somewhat 



1 6 



8 



attenuated caudal extremity is attached, obliquely, a mem- 

 branous, subtriangular suctorial disc, the concavity of which 



