M. M. METCALF ON THE EYES AND SUBNEURAL GLAND OF SALPA. 313 



THE ANATOMY OF THE EYES OF CYCLOSALPA PINNATA, CHAIN FORM. 



The histological structure of the retina of the dorsal eye of the chain 

 form of Cyclosalpa pinnata agrees closely with that of the solitary form, 

 save that no intermediate layer of cells is present between the rods and 

 the pigment cells, i. e., all the cells of the retina except the rod cells have 

 become pigmented. The shape of the eye, on the other hand, differs 

 greatly from that found in the solitary form. There are present in the 

 chain Cyclosalpa pinnata two pairs of small eyes, till now undescribed, 1 

 in addition to the well-known unpaired dorsal eye. 



The Unpaired Dorsal Eye. 



This is situated on the dorsal surface of the ganglion (Plate LVII, 

 Figs. 9 and 10) in a position similar to that occupied by the eye of the 

 solitary form, except that it extends beyond the anterior face of the 

 ganglion, only the posterior third of the eye lying upon the brain (Plate 

 LVII, Fig. 10, and Plate XLIX, Figs. 1 and 2). It consists of two 

 almost distinct portions, the larger of which may be described as a 

 horseshoe with the open side of the horseshoe posterior, differing in 

 this respect from the eye of the solitary form, which has its open side 

 anterior. (Compare Plate LVI, Fig. 7, with Plate LVII, Fig. 9.) The 

 posterior ends of the two posterior limbs are enlarged, as shown in 

 the figure, so that the description "horseshoe-shaped" is not strictly 

 applicable to this portion of the eye. The second smaller portion (e'") 

 lies in the curve of the anterior part of this horseshoe. It is elongated 

 transversely, reaching from one limb of the horseshoe to the other. 

 It is connected to the rest of the eye only by a number of spindle- 

 shaped cells, binding the anterior face of the second mass to the pos- 

 terior face of the anterior portion of the main body of the eye (Plate 

 LVII, Figs. 9 and 10, and Plate XLIX, Figs. 1 and 2). In any one 

 longitudinal section of the eye four or five of these spindle cells appear. 

 This eye, like the eye of the solitary form, lies immediately beneath the 

 ectoderm, in a chamber wholly shut off from the space in which the 

 ganglion lies, except for a narrow opening on the mid-line in front. 

 The optic chamber is, then, a blood space connected with the blood sinus 

 in which the brain lies. In Plate XLIX, Figs. 1 and 2, which are longi- 



'In my preliminary note of this paper [12] I described briefly the structure, 

 position and development of these smaller eyes. 



