INTERMUSCULAR NERVE CELLS OF EARTHWORM 167 



giving rise to some of the free terminations found within the epi- 

 dermis. Kowalski ('09), in referring to the tripolar cells (he 

 apparently did not observe those of the bipolar type), expressed 

 his view as follows: ^^Ces cellules nerveuses profondes, origine 

 peut-etre des terminaisions sensorielles libres intraepidermiques, 

 permettent de rappocher le systeme nerveux des Oligochetes de 

 celui des Polychetes, des Cestodes, et des Mollusques." Dechant 

 ('06), although he recognized both tripolar and bipolar cells in 

 the nerve rings, did not express any definite view as to their 

 significance. In commenting, however, on the theory of the 

 origin of the dorsal spinal ganglion of vertebrates from epider- 

 mal sensory elements which have retreated from their superficial 

 position in invertebrates, he states: 



Es konnen demnach die Sinnesnervenzellen der Wirbellosen mit den 

 Spinal-ganglienzellen der Wirbeltiere gar nicht vergleichen werden, 

 sondern hochstens die Ursprungselemente der freien Nervenendigungen 

 der Wirbellosen mit den Spinalganglicnzellen der Wirbeltiere. Da aber 

 jene noch nicht gefunden sind, so ist ein weiterer Ausbau dieses Ver- 

 gleiches und der strenge Nachweis seiner Richtigkeit der Zeit noch 

 nicht moglich. Unsere nachste Aufgabe wird in der Erforschung jener 

 uns noch unbekannten Zellen gegeben sein. 



Dechant's chief objection to the phylogenetic theory was based 

 on his belief that the free nerve endings in the epidermis represent 

 just 'as primitive a condition as sensory epidermal cells. Von 

 Szuts ('14), on the other hand, who recognized only the two 

 types of bipolar cells, accepts the evolutionary principle and 

 homologizes the intermuscular ganglion cells of the earthworm 

 with the ganglion cells of the dorsal spinal ganglion and 

 ganglion cells of the retina. 



In an attempt to interpret the function and significance of the 

 four types of cells which have been described in this paper, it 

 seems best, since there is little in the way of experimental work 

 which bears directly on this subject, to approach the problem 

 from the evolutionary view-point. In the primitive nervous 

 system, as seen in the Coelenterata, there is usually a receptive 

 epidermal cell which is intimately united by its branching proc- 

 esses with a deeper-lying cell, the gangHon cell or motor cell, 



THE JOURNAL OF COMPARATIVE NEUKOLOGT, VOL. 32, NO. 2 



