154 Dr. A. Metzger on the Male and Female o/'Leriia^a 



XXII. — On the Male and Female of the genus LeniEea hefore 

 the commencement of the so-called Retrograde Metamorphosis. 

 By Dr. A. Metzger *. 



In March 1866 I discovered, on the branchias of Platessa 

 flesus, besides Chondracanthus cornutus, which is usually to be 

 found upon them, a new and extraordinarily elegant Copepod, 

 about one line in length. Subsequent investigations, how- 

 ever, have convinced me that this is to be met with in abun- 

 dance, at almost all seasons of the year, upon every large 

 specimen of the above-mentioned species of fish, but that, 

 from its small size and concealed position, it easily escapes 

 observation. In fact, on the first glance at the branchiae, we 

 observe nothing that could betray the presence of a parasite, 

 except some small dark points and streaks ; and it is only 

 when the branchige are cut out and put into water, so that 

 their individual laminae are separated from each other, that 

 the little parasite is seen, with the free extremity of its body 

 floating at the apices of the branchia?. 



On a careful examination of the different individuals, I could 

 at once distinguish two different forms — a shorter and stouter 

 form, and a slenderer one with an elongated abdomen. My 

 supposition, that in these sexual distinctions were to be seen, 

 was speedily confirmed by the discovery of numerous united 

 pairs. In every such pair the shorter form was always affixed 

 at the base of the abdomen of the slenderer form by means of 

 its strong clasping antenme. I could never find females with 

 egg-threads, notwithstanding my looking for them repeatedly 

 until late in the autumn. As to the systematic determination 

 of this Copepod, which apparently belonged to the Diche- 

 lestiinse, I consequently remained in doubt. 



At last, in April of the following year, I found, contrary to 

 my expectation, the same little animal upon the branchige of a 

 Cyclo-pterus liimpus of not very large size, — and at the same 

 time, on the branchial arches of the same fish, four specimens 

 of a young Lerna'a^ recognizable at the first glance by three 

 cylindrical horns situated on the upper part of the trunk, and 

 also by the abdomen, which had already become somewhat 

 horny and twisted into a sigmoid form ; but how great was my 

 astonishment when, on closer examination, I detected all the 

 characters of my parasite in these LernKOi ! The structm-e 

 of the antennae and limbs, the peculiar fine transverse striation 

 of the abdomen, &c. were so perfectly accordant that I could 

 have no doubt tluit the two fonus belonged to eacli other. As 



* Trant;latfd bv W. S. Dallas, F.L.S. &c., from the 'Arcliiv fiirNatur- 

 Rcschichte,' 18G8, pp. lOG-110. 



