THE EYE OF PECTEN. 67 



not elliptical. Its diameter is a little gi-eater than the cornea, 

 since its periphery extends under the pigment-mantle for 

 a short distance (PI. 6, fig. 1). 



The space in which the lens is suspended is bounded by 

 the connective-tissue wall of the optic vesicle, the subcorneal 

 extension of the same, and by the septum (PL 6, fig. 1, Sep.), 

 a membrane separating the dioptric part of the eye from the 

 retina. This space was regarded by Patten as a blood-space. 

 Carriere (21) first saw the blood-corpuscles in this part of the 

 eye, and Patten, though also finding* them, was at a loss to 

 account for their presence, since the retina seemed to shut off 

 all communication with the blood-lacuna3 of the eye-stalk. 

 Rawitz appears to have found a definite vessel runnino- on the 

 outer surface of the optic vesicle and entering the distal part 

 of the eye ([25], p. 113). Schreiner considers these cor- 

 puscles due to pathological conditions, and remarks that 

 the three other authors named above considered them as 

 normal ([30], p. 17). This is not strictly correct, since Patten 

 stated that they might be forced into the cavity artificially 

 by the conti-action of the connective tissue throuo-h the 

 action of reagents. 



I have only found blood-corpuscles present in this space 

 on extremely few occasions, and on one of these, when there 

 were many, I could trace quite easily a series of spaces in 

 the connective tissue, connecting up the lacunae of the eye- 

 stalk with the lens-cavity. This may of course have been an 

 abnormal condition, and the lacuna may have been produced 

 artificially. These corpuscles had been forced in on the 

 inner side of the eye, and I find no traces of Rawitz's blood- 

 vessel on the outer side. 



The blood plays an important part in the extension of the 

 tentacles, and if a small living Pecten is watched under the- 

 microscope, the corpuscles can be traced running rapidlv 

 along the cavities of the tentacles as they are extended and 

 back in the revei'se direction as they contract. I believe 

 their presence in the eye is due to contraction, and that they 

 are forced there from the lacuniB of the eye-stalk. 



