ETE-SPOT AND PLAGELLTJM IN EUGLENA VIBIDIS. 469 



may be made to Zimmermann *, and to the memoirs of Klebs 

 and Eranze. 



The eye-spot was at first supposed to be a homogeneous red 

 spot or disc ; but Leydig t in 1856 described it in Euglena and 

 some other forms as consisting of scarcely measurable, strongly 

 refractive granules ; and this has since been confirmed by many 

 other observers. 



According to Klebs {I. c.) the eye-spot of Euglena is a well- 

 characterized body, both in form, inner structure, and chemical 

 behaviour. Its form varies with the species, but is very 

 constant for one and the same species. Its structure is appa- 

 rently the same in all species, consisting of two substances — a 

 plasmatic ground-mass forming a fine network, and a pigment 

 which occurs in the form of drop-like bodies embedded in it. 

 The presence of a plasmatic substance can only be inferred from 

 the fact that the eye-spot can be caused to expand under pressure 

 or by the action of swelling reagents, which results in the 

 separation of the pigment-drops from one another. 



Franze {I. c.) states that, in addition to the pigment, the eye- 

 spot contains one or few to many strongly refractive bodies 

 which are, in Tluglena, composed of paramylum, grouped in a 

 more or less regular manner, consisting of a central or excentric 

 " crystal body," with smaller and always more numerous " lens 

 bodies " surrounding it. Both the crystal body and the lens 

 bodies serve to concentrate the light, and the pigment not only 

 absorbs light but s also sensitive to light. 



I have been quite unable to confirm Franze's observations 

 either as to the crystal body or the lens bodies, although it is 

 very easy to observe the granular structure described by other 

 observers. I have examined several species of Euglena and 

 Phacus ; I have had Euglena viridis under observation in all its 

 stages and under many different conditions of its existence, but 

 I have never seen anything of the nature of paramylum bodies 

 in or on the eye-spot. Nevertheless I have sometimes noticed, 

 when examining the eye-spot with a magnifying-power of 500 

 or 600 diameters, an appearance something like that figured by 

 Franze, which seems to be due, however, to the irregular outline 

 of the eye-spot (it is very rarely as regular in outline as Franze's 



* Zimmermann, " Sammel. Eeferate &c., 10. Der Augenfleck (Stigma).'' 

 Beihefte zum Bot. Centralbl. vol. iv. p. 160, 1894. 



t Leydig, Lehrbuck der Histologie. (See Franze, I. c.) 

 LIFH". JOUEN. — ZOOLOGY, VOL. XXVII. 36 



