62 BULLETIN': MUSEUM OF COMPARATIVE ZOOLOGY. 



section (Fig. 4) it is marked by striations which run, roughly spea^king, par- 

 allel to its outer boundary and seem to indicate that it is built up of irreg- 

 ular rods packed closely side by side. A fair number of more or less complete 

 axial sections of this structure have been obtained, but I have only been 

 able to discover one or two fragmentary transverse sections. These show the 

 cut ends of the rods packed together witli a kind of radiating arrangement 

 from the central aperture towards the circumference (Fig. 7). Between tbese 

 rods, nuclei occur very sparingl}'^ and elongated in a direction parallel with 

 the rods themselves. 



4. The Posterior Hemisphere (Figs. 4, 8, jj. h.) occupies the deepest portion 

 of the interior of the organ just within the pigment cup. It has, roughly 

 speaking, the form of a hemispherical bowl with the rim turned inwards. Its 

 thickness is about equal to one-third of its diameter and is such that only a 

 very small spheroidal space is left in the middle of it and is occupied by the 

 end of the internal cone. The thickness is made up of a series of concentric 

 layers which in the sections appear to be slightly separated one from the other, 

 especially near their edges, but this may be an effect produced by the process 

 of cutting. This substance takes up the stain only faintly, and appears to be 

 eomewhat denser in consistency than the inner cup. No nuclei have been 

 noticed anywhere in its substance. 



5. Tlie Internal Cone (Figs. 4, 6, 7, i. co.) is situated with its base against the 

 deeper surface of the lens, whilst its spheroidal apex occupies the internal cavity 

 of tlie posterior hemisphere just described. It is deeply subulate and is bounded 

 by the internal surface of the inner cup. Under a high power it is seen to be 

 composed of finely granular protoplasm, which is niit much affected by the 

 staining fluid. No definite cell boundaries can be seen, but it contains a con- 

 sidtTable number of nuclei. Those near the base of the cone are small and 

 ovoiil in shape, whilst the deeper ones are elongated in the direction at 

 right angles to the axis. Some of them are so long as to occupy a con- 

 siderable portion of the diameter of the cone. A section parallel with the 

 surface of the integument (Fig. 6) just beneath the lens shows that these 

 elongated nuclei have tliuir long axes curved to correspond with a circle 

 drawn round the centre of the cone. They are situated in the deeper 

 layers, whilst the round and ovate nuclei occupy the circumference. 



I have not been able t(j trace the nerve supply to these organs. 



II. SUB-OCULAR OROAXS. 



Beneath each ej'ehall, covered in the living condition by the integument, is a 

 row of five organs, ])lacod at etpial distances from eadi other along the eijuator 

 of tlic Imll (I'latc 10, Fig. 2). They are visible in the living animal (Plate 1, 

 Fig. 3) evidently by nuwon of the transparency of the integument. 



They are ulightly elevated papillae of a clear yellowish-brown color. The 

 three centnil ones are the smallest and are about 0.18 mm. in diameter, 



