M. T. Thorell on the Systematic Position of the Argulidse. 283 



spot, placed on a perfectly similar trilobed projection from the 

 brain -ganglion*. 



We have now gone through the proofs which have been put 

 forward by Kroyer as grounds for the union of the Argulidse 

 with the siphonostomous Copepoda, and shown, we hope, that 

 not one of them can be regarded as in any measure convincing 

 or decisive. We will now briefly recapitRlate the results to 

 which we have been led during the foregoing investigation, and 

 thence arrive at the conclusion respecting the systematic posi- 

 tion of the Argulidse which those results seem to warrant. 



I. The Argulidse correspond with the Copepoda generally, be- 

 sides such points of their organization as are common to the 

 Branchiopoda and Copepoda, only in these particulars : — that 



(1) The females possess receptacula seminis; and that 



(2) Parthenogenesis seems never to occur. 



II. But they differ from the Copepoda generally in the cir- 

 cumstance that 



(1) Their limbs want the intermediate plate (mellanskifva), 

 and do not show the form characteristic of Copepoda ; that 



(2) They have two moveable eyes composed of numerous 

 crystalline stemmata in front of the unsymmetrical larval eye; 

 that 



(3) The integuments of the head are developed into a bi- 

 partite shield, very often covering the larger portion of the body; 

 that 



(4) The eggs are neither attached to external egg-sacs nor 

 are received into a matrix when they leave the ovaries ; that 



(5) Impregnation is not effected by means of spermatophores 

 attached externally to the body of the female ; and that 



(6) The larvae leave the egg in a much more advanced state 

 of development than in the Copepoda. 



III. Meanwhile they agree with the (higher) siphonostomous 

 Copepoda in certain particulars, which all, however, depend upon 

 their parasitic mode of life : they have, for instance, 



(1) A depressed body; 



(2) A pair of the antennae modified as fixing-organs ; 



(3) The mouth transformed into a sucking-tube ; and 



(4) Strongly developed foot-jaws. 



IV. They differ likewise from the Siphonostoma in the follow- 

 ing points : — 



(]) The first, not the second, pair of antennae are the fixing- 

 organs ; 



* Vide Leydig, loc. cit. p. 39 &c. 



20* 



