34: 



THE MICROSCOPE AND ITS REVELATIONS. 



magnifier. The form of Noctiluca is nearly that of a sphere, so com- 

 pressed that while on one aspect (Fig. 297, A) its outline, when projected 

 on a plane, is nearly circular, it is irregularly oval in the aspect (B) at 

 right angles to this. Along one side of this body is a meridional groove, 

 resembling that of a peach; and this leads'at one end into a deep depres- 

 sion of the surface, a, termed the atrium, from the shallower commence- 

 ment of which the tentacle, d* originates, whilst it deepens down at the 

 base of the tentacle to the mouth, e. Along the opposite meridian 

 there extends a slightly elevated ridge, c, which commences with the ap- 

 pearance of a bifurcation at the end of the atrium farthest from the ten- 

 tacle; this is of a firmer consistence than the rest of the body, and has 

 somewhat the appearance of a rod imbedded in its walls. The mouth 

 opens into a short oesophagus, which leads directly down to the great 

 central protoplasmic mass; on the side of this canal farthest from the 



Fig. 297. 



, . jht angles to it: a. 



entrance to atrium; 6, atrium: c, superficial ridge; d, tentacle: e, mouth leading to oesophagus 

 within which are seem the flagellum springing from its base, and the tooth-like process proJ3Cting 

 into it from above; /, broad process from the central protoplasmic mass, proceeding to superficial 

 ridge; <?, duplicature of wall; /i, nucleus. Magnified about 90 diameters. 



tentacle, is a firm ridge that forms a tooth-like projection into its cavity; 

 whilst from its floor there arises a long flagellum, which vibrates freely 

 in its interior. The central protoplasmic mass sends off in all directions 

 branching prolongations of its substance, whose ramifications inosculate; 

 these become thinner and thinner as they approach the periphery; and 

 their ultimate filaments, coming into contact with the delicate membran- 

 ous body- wall, extend themselves over its interior, forming a protoplasmic 



1 The organ here termed ' tentacle ' is commonly designated Flagellum; while 

 what is here termed the flagellum is spoken of by most of those who have recog- 

 nized it, as a cilium. The Author agrees with M. Robin in considering the former 

 organ, which has a remarkable resemblance to a single fibrilla of striated muscle 

 ( 678), as one peculiar to Noctiluca ; and the latter as the true homologue of the 

 flagellum of the ordinary Flagellata. It is curious that several observers have 

 been unable to discoverthe so-called cilium, which was first noticed by Krohn. 

 Prof. Huxley sought for it in at least fifty individuals without success; and out 

 of the great number which he afterwards examined, did not get a clear view of 

 it in more than half-a-dozen. 



