Hbctor F. E. Jungersen: Chordeuma obesum, a new Parasitic Copepod. 17 



the stems of the members of the same pair are connected by a transveree crest, 

 projecting from the ventral side of the segment in question. The rami are flat, oblong, 

 each made up of one segment; the outer ramus (y) is considerably larger than the 

 inner (i) and on the distal part of its inner arched margin beset with four long and 

 stift bristles (in a single case I found five on the third pair) ; at the end of the straight 

 or feebly concave outer margin a fifth short bristle is present. The short and narrow 

 inner ramus (i) is terminally provided with three bristles, of which two belong to the 

 inner, one to the outer margin. The bristles have no plumules, while plumules are 

 present on the two pairs of furcai setæ, of which the inner enes are the longest. 

 There are no furcai appendages, the setæ originating directly from the posterior 

 margin of the telson. 



As the tissues of these larvæ were rather badly preserved, I have not been able 

 to make out inner structural details of any amount, in spite of my transverse and 

 longitudinal sections being quite successful. Distinctly discernible are: the narrow 

 oesophagus leading into the wide intestine (mid-gut), closed behind in the thorax, about 

 at the level of the third pair of swimming feet; and the central nervous system, 

 consisting of the large brain and the ventral ganglionic mass, narrowing towards the 

 first pair of thoracic feet; further back I have not been able to trace it. The presence 

 of antennal or shell-glands as well as of rudiments of genital organs I cannot state 

 with certainty. 



The Cyclops-larva moults and changes into the seventh stage, the parasitic form 

 described sub I. This is sufficiently proved in the case of the male by the faet, 

 already stated, that quite a number of extremely small males — like that represented 

 PI. II, Fig. 26 — have been found together with the ruptured cuticle of the Cyclops- 

 larva, in Bome cases with the tail still lodged inside the latter; and in a single case 

 a very small female was found near an erapty larval cuticle. In all cases observed 

 the formation of a gall was indicated as a condensing of the connective tissue sur- 

 rounding the young parasite and the cast larval cuticle. After the moulting through 

 which the parasitic form^ensues, n(j further moultings take place, but the Copepod 

 and its gall continue for a while to grow considerably ; during the growth the parasite 

 undergoes some slighter modiflcations in shape of body and appendages, as shown 

 above sub I, and develops its inner structures; linally it attains full size and sexual 

 maturity. 



(k>nehidin|^ remarks. 



In »pif*' of the faet that I have had at my disposal only sprciint-ns uf Astrrouyr 

 collected for other purposcs and prrsi-rved for years in spirit, I have been successful 

 enough to find out every step — ho I venture to think nt least — of the meta- 



8 



