;66 



MICROSCOPIC FORMS OF ANIMAL LIFE 



the light ; and its tail-like appendage, whose length about equals 

 its own diameter, and which serves as an instrument of locomotion, 

 may be discerned with a hand-magnifier. The form of Noctiluco is 

 nearly that of a sphere, so compressed that while on one aspect (fig. 

 587, 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 depression of the sur- 

 face ft. termed the atrium, from the shallower commencement of 

 which the tentacle, d. 1 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 tin- 

 appearance of a bifurcation at the end of the atrium farthest from 



FIG. 587. Noctilaca inilit<rin as seen at A on the aboral side, and at 

 B on a plane at right angles to it : a, entrance to atrium ; fe, atrium ; 

 c, superficial ridge ; d, tentacle ; e, mouth leading to oesophagus, 

 within which are seen the flagellum springing from its base, and the 

 tooth-like process projecting into it from above ;/, broad process from 

 the central protoplasmic mass proceeding to superficial ridge ; g, 

 duplicature of wall ; //, nucleus. (Magnified about 90 diameters.) 



the tentacle : this is of 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 tentacle, is a firm ridge that forms a tooth-like 

 projection into its cavity ; whilst from its floor there arises a long 



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

 what is here termed the fltujcUiun is spoken of by most of those who have recognised 

 it as a ciliuni. The Author agrees with M. Robin in considering the former organ, 

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

 one peculiar to Noctilucn, and the latter as the true homologue of the flagellum of 

 the ordinary Flagellata. It is curious that several observers have been unable to dis- 

 cover the so-called cilium, which was first noticed by Krohn. Professor Huxley sought, 

 for it in at least fifty individuals without success ; and out of the great number which 

 he afterwards examined he did not get a clear view of it in more than half a dozen. 



