INTERMUSCULAR NERVE CELLS OF EARTHWORM 157 



Dechant ('06), by means of intravitam methylene blue, suc- 

 ceeded in demonstrating ganglion cells in the nerve rings of the 

 earthworm, but, unfortunately, owing to the fact that he was 

 working with animals which were densely pigmented dorsally, 

 his studies were confined to cells found in the more ventral 

 portions of the earthworm body. For the anterior and posterior 

 nerve rings he found the ganglion cells regularly arranged, usually 

 in groups of three, in the region of the dorsal pair of setae. In 

 the median nerve ring, however, only a single cell was occasion- 

 ally observed in the vicinity of a setal follicle. The cells were 

 of two types, either spindle-shaped and bipolar or triangular 

 and tripolar. In the tripolar cells two processes lay in the nerve 

 ring, while a third much shorter process passed vertically through 

 the circular muscles toward the epidermis. 



More recently tripolar cells have been described by Kowalski 

 ('09) who used Boule's ('07, '09) modification of the silver-ni- 

 trate method of Ramon y Cajal for neurofibrillae. Kowalski 

 describes specifically and figures (figs. 60, 61) two tripolar cells 

 which he refers to as 'cellules sensitives profondes tripolaires.^ 

 Figure 60 represents a cell in the nerve ring, with two processes 

 lying within the ring itself, while from the outer pole a bundle 

 (faisceau) of neurofibrils passes vertically to the epidermis. In 

 figure 61 the tripolar cell lies at the bifurcation of a lateral nerve 

 trunk. One of its processes extends proximally in the lateral 

 trunk while the two others pass distally, one in the dorsal and 

 the other in the ventral portion of the nerve ring. 



Boule ('13), in the course of a detailed discussion regarding the 

 evidence in the earthworm of a correlation between the structure 

 of the nerve cells and the direction of conduction of the impulse^ 

 refers incidentally to both bipolar and tripolar cells in the lat- 

 eral nerve trunks and nerve rings. The tripolar cell (fig. 21) 

 corresponds, in its position and in the extension of its processes, 

 with the one figured by Kowalski ('09, fig. 61). 



In the following year von Szuts ('14), in an extended account 

 of the finer structure of the central nervous system of the earth- 

 worm, failed to make any mention of the tripolar cells observed 

 by Dechant ('06), Kowalski ('09), and Boule ('13). He de- 



