No. 2.] THE MORPHOLOGY OF DERO VAGA. pS i 
have been able to corroborate his statements so far as concerns 
Dero and Tubifex. 
The longitudinal muscle layer (Pl. XIV, Fig. 18, ¢.#zus.) lies 
next the circular and is composed of fibres which are not 
arranged in groups, as in Lumbricus, but are isolated. The 
plasma parts with their nuclei show on the inner side of the 
layer. 
2. NERvous SYSTEM. 
(a) Hestorical. 
Observations have been made on Dero by a number of inves- 
tigators, but little has been written concerning the nervous 
system. Perrier! described the nervous system of Dero obtusa 
(D. perriert), but confined his observations to the dorsal gan- 
glion and the ventral cord. No account was given of lateral 
nerves. 
Reighard? described the nervous system of D. vaga and gave 
an account of the nerves arising from the dorsal ganglion and 
commissure. No mention was made of lateral nerves from the 
ventral cord. He noticed the “lateral line,’ but could not 
trace it as far forward as the dorsal ganglion. 
In 1885 Anton Stole? in a paper on the anatomy and his- 
tology of D. digitata Mill. describes and figures the nervous 
system in greater detail. The dorsal ganglion in the form 
studied has a greater length from front to back than has that 
of D. vaga. The ganglia of the ventral cord correspond in 
shape to those of D. vaga. He figures some very minute 
nerves from the anterior face of the dorsal ganglion between the 
two large nerves and also some from the inner sides of the com- 
missures near their posterior place of fusion. He cites similar 
structures in Stylaria described by Vejdovsky. I am inclined 
to doubt the nervous nature of these fibres, for muscles are 
found in similar positions and I have been unable to find nerves 
1 Edmond Perrier, Histoire Naturelle du Dero obtusa, Archives de Zoologie 
expérimentale et générale, Tome I, 1872, pp. 83-85. 
2 J. Reighard, On the Anatomy and Histology of Awlophorus vagus, Proc. Am- 
Acad. Arts and Scz., Vol. XX, 1884, pp. 101-104. 
8A. Stole, Dero digitata O. F. Miiller: Anatomickaé a Histologicka Studie. 
SB. Bohm. Ges., 1885, pp. 65-95. 2 pl. 
