No. 2.] COMPOUND EYES OF ANNELIDS. 287 



cone itself. From this a central canal extends in some cases 

 into the centre of the cone. 



He states that the consistency and chemical nature of these 

 crystalline cones forbids any idea of glandular structure. 



Near each eye is a lid-like, projecting structure. 



A few years later Claparede (3) figures a large organ at the 

 end of the branchia in Protula Dysteri, Huxley, " hanging like 

 a fruit from a tree," and composed of compressed, pear-shaped, 

 clear cells, 9 fx. in diameter, arranged about a central cavity. 

 Though he knows no function for this organ, I am inclined to 

 regard it as undoubtedly belonging to the same category as the 

 so-called compound eyes, though Huxley (18) had described it 

 as a collection of granular cells, and so that one would infer a 

 glandular rather than a sensory function. In a later work (4) 

 he gives surface views and descriptions of compound eyes in 

 Branchiomma Kbllikeri and Br. vesciculosum, and observes that 

 the former is very sensitive to changes in the amount of illumi- 

 nation, for a slight movement of the hand in the air, at the 

 distance of a metre from the aquarium, causes all the animals 

 to withdraw into their tubes as soon as the shadow falls upon 

 them. Yet Sabellas, having no eyes, remain, he finds, perfectly 

 immobile and unaffected. 



Dalyell had already (l) noted that Amphitrite bombyx is "impa- 

 tient of light," and upon the interception of light instantly re- 

 treats into its tube. 



In the first species the eye is a pyriform mass adnate to the 

 branchia on its concave side near the tip, and presents in sec- 

 tion about thirty crystalline cones, each a pyramidal body 13 fi. 

 thick, with its apex imbedded in the central mass of violet pig- 

 ment. The cuticle over this compound eye is 4 p. thick. 



In the second species the eye is a hemispherical mass, about 

 190 /*. thick, near the tip of the branchia, contains crystalline 

 cones, and is covered by a cuticle of the same thickness as in 

 the former species. 



In Protula intestinum there are four pairs of compound eyes, 

 or rather collections of ocelli, upon each branchia, each ocellus 

 being a spherical lens surrounded by a mass of reddish pigment. 



In the Supplement to the above work, published in 1870, the 

 author describes and figures the compound eye of Branchiomma 

 vigilans, in which the branchia is embraced near its tip by the 



