66 CRUSTACEA—COPEPODA CHAP. 
parasite. The adult organs now begin to be differentiated, as 
shown in Fig. 32, C, from the undifferentiated cellular elements of 
the Nauplius, 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 Naupli 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 Rhizocephala (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, Voto- 
delphys and Agnathaner, possess 
true prehensile antennae.  Ac- 
cording as the parasitism is more 
or less complete, the buccal 
appendages either retain their 
Fic. 33.—Side view of Doropygus pulex, masticatory structure or else 
@, x 106. Abd.t, 1st abdominal become reduced to mere organs 
segment ; Ant.7, Ist antenna; b.p, : S) 
brood- pouch; TZh.1, Ist thoracic of fixation. In Notodelphys both 
appendage ; 7h.4, 4th thoracic seg- sexes can swim actively and retain 
ment. (After Canu.) 
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 
1 Canu, Z'rav. Inst. Zool. Litte. vi., 1892. 
