Mr. T. Brightwell on Hirudo geometra. 11 



II. — On Hirudo geometra, Linn,, and some other species of 

 British Freshwater Leeches. By T. Brightwell of Nor- 

 wich, F.L.S. 



Early in March of the present year (1841), about twenty 

 specimens of a small leech were taken from the back fin of a 

 roach caught in the river Wensum. They agreed generically 

 with the characters given by Savigny of his genus Hamocharis, 

 viz. body cylindrical, composed of indistinct articulations, 

 terminated by large flattish circular* discs or suckers ; head 

 without any toothed tubercles ; eyes four. 



These leeches were from one to two inches long, slender, 

 cylindrical, diminishing in size from the tail to the head; an- 

 terior disc or sucker smaller than the posterior ; colour light 

 brown, with broken rings of a darker colour ; posterior disc 

 with eight or nine small dark spots and brown longitudinal 

 streaks. These characters are nearly those of H. piscium or 

 geometra of authors, the only described species of this genus. 



These leeches being placed with a gudgeon in water, in- 

 stantly attached themselves to the edge of the fins or lip, and 

 remained fixed some days. Being placed by themselves in a 

 glass vessel, and having fresh water put to them every morn- 

 ing, several instances of sexual connexion were observed to 

 take place immediately after the fresh w r ater was added, one of 

 the leeches suddenly twisting itself round the neck of another, 

 and closing upon a longitudinal opening which at this time 

 was very conspicuous in the neck of each. During this union 

 a white substance could be perceived on each side of the part 

 where the bodies were connected. They continued united 

 generally several hours, and in one case during the whole 

 day. When the leeches separated, a white filmy substance 

 was detached from the parts where they had been united, 

 which in one case had the appearance of an egg, but from 

 subsequent observation was found to be part of the film in 

 which the eggs are enveloped. 



Within twenty -four hours after the union took place eggs 

 were deposited, and were found firmly attached to the sides of 

 the glass vessel. By an experiment made with a pair which 

 were kept separate for that purpose, twelve eggs were found 

 to proceed from two individuals. These eggs were semitrans- 

 parent, of a reddish brown colour, oblong-oval, with one end 

 truncated ; they were covered with a white filmy web-like se- 

 cretion, and had longitudinal elevated ridges on the sides. 

 The shells of the eggs were found, on dissection, to be ex- 

 tremely hard. 



* Oblique is the character given by Savigny. 



