Hector F. E. Jungersen: Chordeuma obesum, a new Parasitic Copepod. 15 



The three anterior pairs of swimming feet are bifurcate, the outer ramus with short 

 bristles; the fourth pair is still undivided and small. The ventral crest joining the 

 raembers of each pair of swimming feet in the Copepoda is already distinctly seen. 

 Antennal-and shell-glands are present as before, the latter now the greater. 



e). The following, fifth, stage (Figs. 20, 21), is 0,288-0,312 mm in length; it is 

 to be cailed a Cyclopid (or Copepodid), as the shape now resembles that of a 

 Cyclops in so far, as the abdomen is fully developed, consisting of three distinct seg- 

 ments, and all the swimming feet are biramous, although those of the last pair still 

 are smaller. The antennules (a,) often are held laterally outstretched, the antennæ 

 (aj) pointing fon\'ards. The latter now are slender, unbranched, the last trace of the 

 outer branch having fully disappeared; they are indistinctly three-jointed, the last 

 joint with two terminal setæ. The mandibles are completely lost. The maxillæ are 

 strong, three-segmented, with claw-shaped terminal joint. The anterior three pairs 

 of swimming feet have the outer ramus longer and narrower than in the preceding 

 stage, and the setæ better developed; also the limer branch has grown but is much 

 smaller than the outer, and its setæ are quite small. Fourth pair is short and clumsy, 

 directed backwards and upwards, the rami broad and rounded, the setæ very small. 

 The segmentation of the body and the short tail is distinct; the telson of the latter 

 is flat, and carries in most specimens the two caudal setæ found in all the preceding 

 stages; in some of the oldest specimens two additional small setæ may be seen. The 

 intestine is filled with a large oil-drop, and ends blindly in the thorax without reaching 

 the abdomen. The ventral nervous system now does not show any distinct ganglia; 

 it is condensed into a mass, broad behind the moulh, pointed backwards between the 

 first pair of thoracic feet. Antennal-and shell-gland are as in the preceding stage. 



The cyclopid stage is the last stage of metamorphosis which I have found enclosed 

 in the matemal gall; in some specimens, however, I have seen inside the cuticle of 

 its antennules a new antennule resembling very much that of the larval stage, found 

 outside the gall; it seems therefore pretty certain, that the Cyclopid will change into 

 the sixth stage, f) the Cyclops-larva (Figs. 22 — 24). This stagt? has been found 

 either attached to the walls of the bursal pouches in Asteronyx or loosely imbeddetl 

 in the connective tissue of these walls. Probably the moulting, which produ<-oH this 

 larva, takes place inside the matemal gall; soon after emcrging the larvæ then l«'nvo 

 the gall — in which way I am not able to state; there is no rcgular previously formcd 

 opening on the capsule, fit for escaping, and no structure in the larvn seems spiH'ially 

 adapted for boring through any tissues. Oncc escaped fnin tli. n-.Al ih. 1m\ . prob- 

 ably either settle again in the same host, in which th«»y were ruisod. ur thoy mak«* 

 their way out, seeking to infest other individuals of Asteronyx. In the first rasi« (h«»y 

 add to the stock of parasites alntady pn'Hont: thus wc easily inight cxphiin, why some 



