1907.] NATURAL SCIENCES OP PHILADELPHIA. 107 



fourtli and fit'th trunk sc2;monts. Two commissures here join the 

 ventral cords with one anotiier. Hetweeu this ))air of ganglia and the 

 precetling, in the left ventral nerve cord, another opening or fenestra 

 is seen in fig. 1. Between the fifth and sixth segments is the fourth 

 pair of ganglia, again united l)y two transverse commissures, but pos- 

 sessing only a very few scattered ganglion cells. Posterior to this point, 

 the ventral nerve cords, which have been gradually tapering caudad, 

 suffer a sudden diminution in calibre. A fifth pair of ganglia in the 

 sixth segment is possibly indicated by the presence of three or four 

 ganglion cells on each side. 



Nerves given off laterad from the ventral cords to the hypodermis 

 were not observed, but this by no means argues their absence, since in 

 the nature of the case the}' w^ould be difficult to observe, unless of 

 considerable size. 



(6) Sense Organs. — The Eyes. — These organs are situated, as 

 shown in text fig. I, on the dorso-lateral surface of the head, about 

 midway between its anterior tip and the second ciliated ring; their 

 distance from one another is about one-half of the width of the head 

 at this point. Their structure is essentially the same as that described 

 for the eyes of other members of this group (fig. 10). Each consists of 

 a cup-shaped mass, composed of reddish pigment granules, the mouth 

 of which encloses a subspherical lens, slightly bilobed, the two lobes 

 separated by a well-marked partition. Below the lens, in the lower 

 part of the pigment cup, is a small space filled with a colorless fluid. 

 Each eye is directed forward and outward, and lies embedded in the 

 hypodermis ca. 4 ti below its outer surface. The cellular structure of 

 the eye is not clear. Although the lens is sharply divided into two 

 lateral halves, and in some cases the pigment cup faintly so, no nuclei 

 are discernible within the eye itself, even when depigmented, nor could 

 the eye be definitely connected wdth any of the adjacent cells. About 

 the base of the pigment cup are clustered a number of ganglion cells 

 belonging to the dorso-median group; it would perhaps be more correct 

 to say that the base of the pigment cup is embedded in this group. 

 Some at least of these cells, on account of their position, must func- 

 tion as percipient elements, although no differentiation serving this 

 end could be observed. Korschelt (1SS2) describes a distinct optic 

 nerve, connecting the eye with the brain; on the other hand Weldon 

 (1886), Harmer (1889a) and Schimkewitsch (1895) all agree that, in 

 the species studied by each, the eyes are embedded in the dorsal por- 

 tion of the brain. 



/Sense Hairs. — .Much time was spent in searching for these before 



