NOTES ON NOCTILUCA. 327 



The spliei'e walls are of crystalline transparency, and the 

 animal measures in its longest diameter in full-grown speci- 

 mens about -^th of an inch. 



From the bottom of the atrium and near to one end of it 

 there springs a long ribbon-like vibratile flagellum (d). 

 Here the atrium is very shallow, but towards the opposite 

 end it becomes rapidly deeper. It is just outside this deeper 

 end that the superficial ridge just mentioned commences. 



At the root of the flagellum is situated the mouth (e), a 

 rather wide aperture in the floor of the atrium. It opens 

 into a short gullet, which leads down into an irregular mass 

 of granular protoplasm situated in the interior of the animal 

 at a little distance from the central point of the body, and 

 immediately beneath the floor of the atrium. Running along 

 the inner side of the gullet walls opposite to the root of the 

 flagellum is the ridge first pointed out by Huxley,^ which 

 near its middle projects in the form of a tooth into the cavity 

 of the gullet. The gullet further contains a single long 

 cilium first described by Krohn f this springs from its floor 

 and is kept in a state of constant vibration. The floor of 

 the gullet is formed by the central mass of protoplasm, 

 here naked and in direct contact through the mouth and 

 gullet with the surrounding medium. Near the root of the 

 cilium is a depression in the floor which can be followed for 

 a Httle distance into the protoplasm. 



The central protoplasm mass sends oif in all directions 

 long, branched, frequently intercommunicating processes of 

 its substance which radiate towards the circumference of the 

 sphere, becoming thinner and thinner as they recede from 

 the centre, until finally, as exceedingly delicate filaments, they 

 reach the sphere-walls with Avhich the extremities of their 

 ultimate ramifications become confluent. 



Besides these branching thread-like processes there is sent 

 off from the central protoplasm a broad irregularly quadran- 

 gular thin process (figs. 2, 3,/'),which extends to the superficial 

 ridge, to which it becomes attached by one of its edges ; its lower 

 free edge has the form of a thickened border, and at its upper 

 edge it becomes continuous with a plate-like striated struc- 

 ture ((/), which I believe represents a peculiar duplicature 

 of the body-walls. In contact with the protoplasm mass is a 

 clear spherical body {h) , the nucleus about -rsVu th of an inch 

 in diameter. 



The sphere walls are composed of two membranes, an 

 external one thin, transparent, and structureless, and an 



1 ' Quart. Journ. Mic. Sc.,' vol. iii, 1855. 

 - Wiegmann's ' Arcbiv,' 1852. 



