416 University of California Publications in Zoology. [V L - 6 



17). Of these, the two lateral pairs are derived from the primary 

 longitudinal stems, each divided into two and continued pos- 

 teriorly from the ganglionic knots. The two lateral connectives 

 of each side are interconnected by anastomosing branches, lateral 

 and irregular, nearly parallel to the proximal ring, and fre- 

 quently quite as heavy. The dorsal and ventral median pairs, 

 lying in the median third of the funnel wall, extend only from the 

 proximal ring to the distal ring. From the distal ring branches 

 run out into the frills at the points where the longitudinal con- 

 nectives enter the ring. 



Distribution of Ganglion Cells. No attempt has been made 

 to deal with the histology of the nervous system, further than 

 is necessary for understanding the significance of the structure of 

 the ganglionic knots at the lateral margins of the anterior and 

 posterior commissures. The nerve stems, both longitudinal and 

 peripheral, are composed of exceedingly delicate fibrils, woven 

 together in a dense meshwork (pi. 34, fig. 16). Around the stem 

 is a covering of nucleated parenchyma fibres, or sheath cells. 

 There are no nuclei within the meshwork. At intervals along the 

 two main lateral stems, where branches are given off, there appear 

 just inside these ''sheath cells" a cluster of cells having homo- 

 geneous cytoplasm and oval, clear nuclei, with a few chromatin 

 nucleoli (gang. 1st., pi. 44, fig. 67). These correspond to the 

 "first type" of ganglion cells described by Pintner (1880) and 

 by Niemiec (1886). They occur only at the margins of the main 

 lateral nerve stems and in the nerve rings : the anterior ring, the 

 proximal and distal ring commissures. In the ganglion knots 

 there occur very large cells, with coarsely granular, intensely 

 staining cytoplasm, and a large, clear nucleus containing one 

 large and several small chromatin nucleoli (pi. 44, fig. 66) . With 

 Lyon 's blue these cells stain a dark violet blue quite distinct from 

 the clear "Himmelblau" as Lonnberg calls it, of the the fibrous 

 tissue. These occur only in the ganglion knots of the anterior 

 and posterior bridge commissures, not at all in the median sec- 

 tions of the commissures, in the rings, or lateral stems. They are 

 not numerous, their total number not exceeding seventy or eighty. 

 They correspond to the second type of cells described by Pintner 

 and by Niemiec, commonly referred to as giant cells. 



