66 CRUSTACEA COPEPODA chap. 



parasite. The adult organs now begin to be differentiated, as 

 shown in Fig. 32, 0, from the undifferentiated cellular elements of 

 the N^auplius, the future adult organism being enclosed in a 

 spiny coat from which it escapes. At this stage it occupies a 

 large part of its host's body, lying in the distended ventral blood- 

 vessel, and it escapes to the outside world by rupturing the body- 

 wall of the worm, leaving behind it the second antennae, which 

 have performed their function as a kind of placenta. Malaquin, 

 to whom we owe this account, makes the remarkable statement 

 that if two or three Monstrillid Nauplii develop together in the 

 same host they are always males, if only one it may be either 

 male or female. The only parallel to this extraordinary life- 

 history is found in the Ehizocephala (see pp. 96-99). 



Fam. 5. Ascidicolidae.^ — Although the members of this 

 family, which live semiparasitically in the branchial sac or the gut 



of Ascidians, betray their Am- 

 pharthrandrian nature by the 

 sexual differences of their first 

 antennae, only two genera, Noto- 

 delphys and Agnathaner, possess 

 true prehensile antennae. Ac- 

 cording as the parasitism is more 

 or less complete, the buccal 

 appendages either retain their 

 Fig. 33.— Side view of Doropygus puhx, masticatory Structure or else 

 9, X 106. AMI 1st abdominal become reduced to mere organs 



segment ; Ant.l, 1st antenna ; 6.^3, _ ^ 



brood - pouch ; Th.i, 1st thoracic of fixation. In Notodeljpliy s both 

 'S^T^'iLT *'"'''' "'" sexes cairswim actively and retain 



normal mouth-parts ; they live 

 parasitically, or perhaps commensally, in the branchial cavities of 

 Simple or Compound Ascidians, feeding on the particles swept 

 into the respiratory chamber of the host. They leave their host 

 at will in search of a new home, and are frequently taken in the 

 plankton. 



Doropygus (Fig. 33), a genus widely distributed in the North 

 Sea and Mediterranean, also inhabiting the branchial sac of 

 Ascidians, is more completely parasitic, and the female cannot 

 swim actively. Forms still more degraded by a parasitic habit 

 are Ascidicola rosea (especially abundant in the stomach of 



^ Canu, Trav. Inst. Zool. Lilte. vi., 1892. 



