Ch. XXIII.] NOOTILUCiB. 397 



motion, to be minute Entomostracous Crustacea. They 

 "were so minute that, by the imperfect light on board ship, 

 I long tried in vain to secm-e one to place imder the micro- 

 scope. Besides these were also some larger species of 

 Entomostraca. 



The Noctilucee maybe described from these specimens: — ■ 

 they measured from ,-sy5 to xrs- oi an inch in diameter ; 

 they. were somewhat kidney-shaped, and of a pale greenish 

 colour when seen with the naked eye, closely resembling 

 Volvox in appearance, but with a much less active move- 

 ment. They had, however, powers of locomotion, though 

 the means were not apparent under the microscope. They 

 had a dark nucleus, usually irregular, but in some cases 

 spherical and well defined. The circumferential outline 

 seemed very faiut (on account of their globular form), and 

 their general aspect was very variable. A kind of sHt ap- 

 peared, to extend through two-thirds of the body, from which 

 faint lines radiated, usually having a double outline, and 

 not reaching the circumference of the sphere, but often 

 termidating in large, round,' granular bodies of various sizes. 

 The whole body was studded with minute spherical inter- 

 spaces (vacuoles) of various sizes, which strongly refracted 

 the light, like oil globules; but slight movements, which 

 appeared to be taking place in an almost imperceptible 

 manner, soon changed the whole aspect of any individual 

 Noctiluca while under observation, so that the description 

 or drawing of one minute did not answer for the next. Each 

 Noctiluca had a large curved cUium projecting beyond the 

 body, by means of which they are believed to move, ap- 

 parently taking its rise from the nucleus. 



The form of luminosity due to Noctilucas, although very 

 striking, yet, owing to its softness, appears to be completely , 



