160 BULLETIN OF THE 



two defiuite lines whose significance will be considered later. (Cf. Plate 

 VI. Figs. 72-88.) 



Tlie large ganglion cells so far surpass in size those of the first kind 

 tliat they might well be called giant cells were it not that the name 

 implies a homology which I do not wish to affirm. There are in all 

 live pairs of these large cells, which are nearly constant both in position 

 and in size. Figure 94 (Plate VIII.) represents them diagrammati- 

 cally and from a comparison of this with Figure 63 (Plate V.) the dif- 

 ferent cells may be recognized at once. It will be convenient in the 

 description to designate them by numerals, beginning with the most 

 anterior pair. 



Since the chief characteristic of the cells of the second class taken as 

 a whole is the nucleus, I shall begin with a description of this struc- 

 ture, which is relatively very large and somewhat irregular in form 

 (Plate V. Fig. 69). It never stains deeply, and shows one or more clear 

 vacuolated areas. The nuclear membrane is delicate, and the chromatic 

 substance finely distributed in lines or rows of dots. The nucleoli vary ; 

 sometimes (PI. VII. Fig. 95, cl. gn. III.) none are present, and again 

 there are (Fig. 95, cl. gn. V.) one or two very prominent ones, or in 

 other cases (PI. V. Fig. 69) a number of smaller ones. Frequently, one 

 finds within the nucleus structures (Fig. 69) of an irregular appearance 

 surrounded by a clear space of varying width, and bounded externally 

 from the surrounding nuclear matter by a very definite line. It ap- 

 pears as if the irregular bodies had originally filled the clear space or 

 vacuole, and had shrunken away from the enveloping nuclear matter in 

 the process of preservation. Exactly similar structures occur in the 

 nuclei of the dorsal cells to be described, as well as in the nuclei of the 

 large cells in the anal ganglion : whatever the nature of these enclosures 

 may be, they seem to be characteristic at least of the larger ganglion 

 cells. I do not know that similar bodies have been found in ganghonic 

 cells of other animals. 



The amount of protoplasm which surrounds the nucleus in the five 

 pairs of large ganglion cells varies, somewhat in relation to the position 

 occupied by the cells. The cells of the most posterior pair (Fig. 95, 

 cl. gn. v.), which protrude above the mass of the brain, have a consid- 

 erable amount of cell protoplasm ; those of the third pair (Fig. 95, 

 cl. gn. III.), which are only partly surrounded by fibres, show a lesser 

 quantity, while the others, which are deeply embedded in the fibrous 

 substance, have merely a thin mantle of protoplasm surrounding the 

 nucleus. 



