212 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



First, no larvse have ever been found fastened by their frontal 

 margins. Nordmann was fortunate enough to discover a cr^wd of 

 the copepodid larvse chnging to the roof of the mouth of a perch. On 

 removing them and placing them in water, it was found that some 

 swam around vigorously in the water while others crawled about by 

 means of their maxillipeds." The former had probably just found 

 the fish, while the latter were ready to attach themselves. 



Considering that the locomotor organs of these latter, in bringing 

 them to the fish, have entirely served their function and are to degen- 

 erate and disappear at once, it seems probable that they cease activity 

 as soon as the larvae are once fastened to their host, and become 

 practically useless before the moult occurs. At all events, none of 

 these larvse were fastened to the fish by their frontal margins, for 

 this would scarcely have escaped Nordmann's observation. 



The present author has secured every copepodid stage from the 

 adult down to one which was shorter than the free-swimming form 

 just described, and mto which the latter molts. But this larva was 

 fastened by the tips of the second maxilla? and not by the frontal mar- 

 gin. Again the second maxillae, when first found with the filament 

 attached to them, are too short to reach the frontal margin. We 

 can easily understand how at the time of attachment, while the larva 

 is still clmging with its maxillipeds, it could pull its body forward, 

 after the end of the filament was attached to the gill arch, far enough 

 to allow the maxilla? to grasp it. But it is not easy to see how these 

 maxillae could get hold of the filament after the larva had once cast 

 itself loose from the fish and was hanguig by its frontal margin. 

 Since the second maxillae are to serve as attachment organs through- 

 out life, there is every reason why the transference should be made 

 at once and no excuse to offer for the postponement of it. 



SECOND COPEPODID STAGE. 



BODY FORM. 



Claus predicted for this stage a larva in which the number of body j 

 segments was not increased, the mandibles were inclosed in the I 

 mouth-tube, and the setae of the swimming legs had degenerated. 

 He was unable to find such a theoretical larva, but it can now be ! 

 presented, and the closeness with which it conforms to his prediction | 

 proves the accuracy of his interpretation. 



This larva is actually shorter than the free-swimming form, owing , 

 to a refusion of the segments there separated (fig. 28). i 



The body has been much thickened dorso-ventrally, so that it is 

 no longer flat but cylindrical, while the thorax and abdomen have 

 been relatively enlarged, and all the joints have stiffened so as to be 

 practically immovable. 



« Mikrographische Beitrage, zweites heft, p. 84. 



