ORIENTATION IN COLONIAL ORGANISM 7 



extends entirely around the zooid and is continuous with the 

 strands which connect them with each other (fig, 1). This layer 

 of substance is more distinct in living colonies than in sections. 

 Thus it is highly probably that all of the eye-spots in a colony 

 have protoplasmic interconnections. 



Superficially these eye-spots are very much like the primitive 

 eyes in turbellaria and Amphioxus as will readily be seen by com- 

 paring figures 3 and 4 with figures 5 a and b. In the latter the 



ooJmm 



Fig. 3 Camera sketch of a section of Gonium taken pei'pendicular to the 

 plane of the colony showing three zooids. Sections S/j. thick. No. 6 compensat- 

 ing ocular and iV homo, oil immersion objective. Enlarged 4 diameters with 

 pantograph, e, eye-spot; p, pyrinoid; n, nucleus; 7nm, projected scale. The eye- 

 spot consists of an opaque saucer shaped structure and, a hyaline lens-shaped 

 bodj^ It is less than l/x in diameter. In the zooid to the left the razor passed 

 nearly through the middle of the eye-spot; in the other two zooids it passed a 

 little to one side of the middle, consequently the hyaline part appears relatively 

 smaller in these. Drawn by Caswell Grave. 



opaque part appears to function in restricting to certain areas, 

 the field from which the sensitive hyaline position received light. 

 Thus they seem to function as direction eyes. The eye-spots 

 probably function in the same way. At any rate, these bodies in 

 many species are so well differentiated and so similar in their 

 structure and position in different individuals that they can not 

 be looked upon merely as accumulation of waste products as is 

 maintained by a considerable number of investigators. 



