74 THE VOYAGE OF H.M.S. CHALLENGER. 



intestine exliil)its very energetic and uninterrupted peristaltic and antiperistaltic move- 

 ments, giving it a peculiar moniliform aspect. 



Circulatory System. — The heart (PL XL figs. 5, G, /;) is placed immediately beneath 

 the posterior part of the carapace, and exhibits a structure very similar to that observed 

 in the higher Podophthalmia, being rather concenti'ated, of a somewhat short polygonal 

 fonii, and furnished with six ^^airs of fissiform venous openings, for the entrance of the 

 blood accumulated in the pericardial sinus. Moreover, the number and arrangement of 

 the principal arterial trunks would seem to agree perfectly with that observed in higher 

 Crustaceans. 



Generative System. — The ovaria (PL XL fig. 5, ov) form two partly connate masses 

 of a somewhat irregular ovoid form, placed beneath the heart, and projecting anteriorly 

 to a greater or less extent above the liver. They are found to contain numerous, 

 perfectly translucent egg-cells which vary in size, and from their lower face give origin 

 to two rather strong oviducts, extending straight downwards and opening close 

 together on the sternal part of the antepenultimate segment of the trunk. Here, too, 

 may often be seen afiixed two pedunculated vesicles, the spermatophores (PL XIIL 

 fig. 7). 



The testes are combined as a comparatively small bunch of rounded, anteriorly point- 

 ing cseca, lying in front of the heart, immediately beneath the carapace. The vasa 

 deferentia are very long and flexuouse, extending posteriorly into the last segment of the 

 trunk, where they curve abruptly downward, and form a considerable dilatation (see 

 PL XL fig. 4), within which may be observed the developing spermatophore. The 

 latter exhibits in the present genus (see PL XIL fig. 23) a somewhat lageniform 

 appearance, being gradually dilated toward the apex, and possessing a highly chitinised 

 envelop. The spermatozoids constitute simple, elliptical, nucleate cells. 



Habitat and Distribution. — All the known species of this genus are triily pelagic, 

 the animals being often found in great profusion swarming at the surface of the sea, 

 especially at night ; but in all probability they descend at times to considerable depths, 

 as is alleged to be the case with most other pelagic animals. 



The genus would seem to be distributed throughout most parts of the ocean, except 

 perhaps the Arctic region, where it is represented by a closeh' allied generic type, 

 Boreoiohaiisia, G. 0. Sars. 



