74 



NATURAL HISTORY OF ARTHROPODS. 



generic name from its remarkable optical organs, the facets of which cover the whole 

 of the upper surface of the head. Cystosoma is a closely related form, which was 



Fig. y9. — 77;a'«»fcjJSj>e//«ci(/a, a little reduced. >-■ l^pper surface of head, slio'wing 

 the large eyes. 



found off the Cape Verdes, at a depth of fifteen hundred fathoms. For these two 

 forms a family, Cystosomid.e, has been erected. 



Tlie Hypekid^e are represented on our coast by two or more species, which possess 



commensal habits. One of these inhabits the 

 genital folds of Aurelia, Cyanea, and other 

 jelly-fishes, but it is not compelled to stay there, 

 for it is a good swimmer, and leaves its host 

 whenever it wishes. All of the forms belong- 

 ing to this family have a very thin integument, 

 which is free from hairs ; the antennulie are 

 present in both sexes ; the eyes are very large. 

 They are found in all parts of the \\'orld, and 

 many have the same habits as the species mentioned above, some affecting jelly- 

 fishes, others living with Balpoe, etc. Some of the European species find a home in 



Fig. 100. — Hyperia, enlarged. 



