1914] Little: Ocelli of Pohjorchis 317 



to be a simple continuation of the ends of the pigment cells. No 

 pigment was found in that of Pohjorchis. Although in some sec- 

 tions the lens in Polyorcliis appeared to be the continuation of 

 the cells of the eye. in others the line of demarcation seemed clear 

 cut, so that no final eonelu.sion could be drawn as to its relations. 

 The fact that the lens easily broke loose in macerations and 

 appeared as a biconvex body might point to its being a separate 

 structure and perhaps a modification of the cuticle. 



The peripheral nervous system of Pohjorchis has its main loca- 

 tion in the subumbrella and tentacles, and resembles that of the 

 general type of medusoid forms. According to Chun (1902) and 

 Eomanes (1898) the lower forms of medusae have only a few 

 nerve or ganglion cells scattered beneath the surface, with no indi- 

 cation of gathering to form continuous strands. This is especially 

 true in the lower Anthomedusae. In the Leptomedusae, however, 

 a higher development is found in that the bipolar nerve cells meet 

 in their end processes, which lie adjoining each other, to form a 

 sort of cord or nerve ring at the base of the bell. Interspersed 

 at intervals along the cord are multipolar or ganglion cells. These 

 may be massed in groups of from two to several to form ganglia. 

 This is shown in TAzzia (see Hertwigs, 1878), in which the ten- 

 tacles are grouped in four bunches of eight each. At the base 

 of each of these sensory bulbs the nerve cord becomes much 

 swollen and a number of ganglion cells accumulate here. The 

 nerve ring lies entirely in the ectoderm between the layer of 

 muscle fibers and the epithelium. It usually consists of two parts, 

 the upper and lower, separated by branches of the connective 

 tissue, though Linko (1900) reports in Catablema only a single 

 region. This separation into two parts is only an incomplete 

 division, as in most forms are found small fibers or strands pierc- 

 ing the membrane between the two parts and thus partially 

 uniting them. Agassiz (1849) says in describing Sarsia: "The 

 nervous system consists of a simple cord of a string of ovate cells, 

 forming a ring around the lower margin of the animal, extending 

 from one eye-speck to another, following the chymiferous tube, 

 and also its vertical branches, round the upper portion of which 

 they form another circle. . . . Prom the upper ring threadlike 

 cells are traced downward along the proboscis." In Sarsia is 



