NOTODELPHYID^. 123 



the head, fourth and fifth segments in the female 

 mostly coalescent, and forming the envelope of the 

 ovisac. Anterior antennae composed of from five 

 to fifteen segments ; posterior 3- jointed, simple, and 

 terminating in a strong claw or in several curved 

 setse. Mandibles strongly dentated and provided with 

 a 2-branched palp. Maxillas composed of a biting 

 portion, from which spring several short laminas 

 fringed with branchial filaments. Two pairs of foot- 

 jaws somewhat similar to those of the Cyclopidse. 

 First four pairs of feet adapted for swimming and 

 2-branched ; fifth pair small or altogether absent. 

 No external ovisac, the ova being matured in a pouch 

 formed by the integument of the enlarged fourth 

 segment of the thorax. 



The animals belonging to this family are found 

 almost exclusively in the branchial sacs or body 

 cavities of the simple (or rarely of the compound) 

 Ascidians. They are not true parasites, not being pro- 

 vided with any suctorial apparatus, moving about quite 

 freely within the body of the host, and not attaching 

 themselves in any way to its tissues. They are, indeed, 

 in all probability, Cyclopidae, which have become 

 modified in build by their inactive habits and the 

 restricted boundaries of their dwellings. It is evident 

 that under these conditions the long antenna and 

 limbs of the free-swimming species would be an 

 encumbrance, or at any rate could be of very small 

 service, and one would almost be inclined to believe 

 that these appendages must still be in course of 

 degradation owing to constant disuse. The clasping 



