754 OBSERVATIONS ON SOME AUSTRALIAN POLYCII^TA, 



The eyes are rather complex in structure, like the eyes of many 

 annelids, but have no lens, consisting of a thick-walled spheroidal 

 capsule opening on the exterior ; the wall of the capsule is 

 composed of a layer of pigmented cells continued internally 

 into radiating elongated cones the bases of which are external, while 

 the curved, pointed apices line the central cavity. In complexity of 

 structure the eye of Halla, though ranking higher than that of 

 many Polych^eta, yet falls considerably below that of such forms as 

 Toniopteris (ly and Alciope (2) ; it bears a very strong resemblance 

 to tlie eye of Pecten as described by Van Haren Roman (" Voyage 

 of the Willem Barents," Die Lamellibranchiaten, p. 17.) 



Embedded in the substance of the nerve cord in all the speci- 

 mens I have examined, in the third to the eighth segments, are a 

 series of eight or ten oval vesicles, ijjth of an inch in diameter. 

 These are enclosed in a capsule of fine fibrous tissue with small 

 nuclei, except at one point where a bundle of nerve fibres 

 enters the interior. The capsule is filled with finely granular 

 material, and contains a second smaller spherical vesicle, 

 about a fourth of the size of the larger one. This smaller 

 vesicle is more homogeneous than the larger one, and contains in 

 its interior a spherical solid body, which stains darkly with 

 hsematoxylin. I have been unable to determine the nature of these 

 bodies. In structure they have the appearance of very large cells 

 with nuclei and nucleoli, and might be supposed to be encysted 

 unicellular parasites, but the constancy of their presence, and, 

 more particularly, the passage into their interior of a bundle of 

 fibres from the nerve-cord, seem to point to their being essential 

 parts of the animal : they may be a rudimentary form of otocyst. 



(1) Vide Vejdovsky, " Beitriige zur Kenntniss der Tomopteriden " 

 Zeitschr.f. wiss. Zool XXXI. Bd., p. 81. 



(2) Greef, "^ Ueber die Augen insbesondere die Retina der Alciopiden," 

 Sitzungsb. derGesellsch. zur BeforderungdergesammtenNaturwissenschaften 

 zu Marburg, 1875, pp. 116-138. 



