6 S. O, MAST 



hyaline »substance, globular or lenticular in form and a brownish 

 opaque substance frequently somewhat cup-shaped. The latter, 

 it is held, usually surrounds the former more or less completely. 



Thus it appears that these structures resemble, somewhat, the 

 eyes in turbellaria, rotifera and copepoda, and this is largely re- 

 sponsible for the conclusion frequently stated that the former are 

 homologous with the latter. Franze('93, p. 162), however, op- 

 poses this contention. He says: ''Die Augen der Turbellarien 

 und Rotatorien sind keine Homologa der Stigmata, sondern die 

 ausserliche Ahnlichkeit beider Differenzirungen wird durch die 

 gleichen Funktionen bedingt." He, in common with a large pro- 

 portion of other investigators, holds that the eye-spots function 

 as light recipient organs. 



While much of the work on the structure of the stigmata has 

 been thorough, it was our opinion that with the application of 

 modern histological technic it might be possible to discover ele- 

 ments in them that would throw light on their nature and func- 

 tion. With this in view colonies of Gonium and Eudorina were 

 fixed in Bouin's and Fleming's fluids. Some were embedded in 

 paraffin and cut into sections 2/i and 3^ in thickness and stained 

 with iron haematoxylin and safranin. Others were mounted 

 whole, some stained and some not. These preparations were 

 thoroughly studied with a combination of No. 6 Comp. ocular 

 and 2 mm. Apoch. Homog. Immersion objective and briefly w4th 

 more efficient combinations. It was found that the eye-spots 

 both in Gonium and in Eudorina consist of two parts, an opaque 

 cup-like structure and a lens shaped hyaline structure (figs. 3 

 and 4) but no further details could be seen in them although the 

 best lens systems made were used. This, of course, does not 

 prove that there is no finer structure present. It merely indi- 

 cates that if there is, it is ultra microscopic. 



By referring to figures 3 and 4 it will be seen that the eye- 

 spots in Eudorina are considerably larger than those in Gonium. 

 These figures indicate that they are situated at the surface of 

 the zooids with the hyaline portion outside. Gareful observa- 

 tions seem to indicate that there is a thin protoplasmic layer, not 

 represented in the figures, which is outside of this structure and 



