FIG. 32.—Later stages in the development of _Haemocera danae_. _Abd_, Abdomen; _Ant.1_, _Ant.2_, 1st and 2nd antennae; _ch_, chitinous investment; _e_, eye; _Ect_, ectoderm; _En_, endoderm; _Mes_, mesoderm; _Mes & en_, mesoderm and endoderm; _R_, rostrum; _St_, mouth and stomach; _Th_, thoracic appendages. (After Malaquin.) ] [Illustration: FIG. 33.—Side view of _Doropygus pulex_, ♀, × 106. _Abd.1_, 1st abdominal segment; _Ant.1_, 1st antenna; _b.p_, brood-pouch; _Th.1_, 1st thoracic appendage; _Th.4_, 4th thoracic segment. (After Canu.) ] =Fam. 5. Ascidicolidae.=[46]—Although the members of this family, which live semiparasitically in the branchial sac or the gut of Ascidians, betray their Ampharthrandrian nature by the sexual differences of their first antennae, only two genera, _Notodelphys_ and _Agnathaner_, possess true prehensile antennae. According as the parasitism is more or less complete, the buccal appendages either retain their masticatory structure or else become reduced to mere organs of fixation. In _Notodelphys_ both sexes can swim 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 _Ascidiella scabra_ at Concarneau), in which the female has lost its segmentation, the mouth-parts and thoracic legs being purely prehensile, and various species of _Enterocola_, parasitic in the stomach of Compound Ascidians, in which the female is a mere sac incapable of free motion, while the male preserves its swimming powers and a general _Cyclops_-form (Fig. 34). We have here the first instance of the remarkable parallelism between the degree of parasitism and the degree of sexual dimorphism, a parallelism which holds with great regularity among the Copepoda, and can be also extended to other classes of parasitic animals. [Illustration: FIG. 34.—_Enterocola fulgens._ =A=, Ventral view of ♀, × 35; =B=, side view of ♂, × 106. _Abd.1_, 1st abdominal segment; _Ant.1_, _Ant.2_, 1st and 2nd antennae; _c.m_, gland-cells; _n_, ventral nerve-cord; _og_, oviducal gland; _ov_, ovary; _po_, vagina; _Th.1_, 1st thoracic appendage; _Th.4_, _Th.5_, 4th and 5th thoracic segments. (After Canu.) ] [Illustration: FIG. 35.—_Asterocheres violaceus_, ♀, with egg-sacs, × 57. (After Giesbrecht.) ] [Illustration: