LEWIS. — POLYCH^TE ANNELIDS. 259 



Before concluding this paper I would take the opportunity to express 

 my sincere gratitude to the director of my studies, Professor E. L. Mark, 

 for the assistance and advice which I have constantly received from him. 

 And I would gratefully acknowledge my indebtedness to the officials of 

 Radcliffe College for the encouragement which they have given me in 

 my work, and to the Society of Collegiate Alumna3 for the aid I have 

 received from them in the form of a fellowship. 



IV. SUMMARY. 



1. Confirmation of the view that Leydig's fibres in annelids are true 

 nerve fibres ; that the sheath of Leydig's fibre is comparable to the me- 

 dullary sheath of nerve fibres in vertebrates ; that the contents are com- 

 parable to the axis cylinder; and hence, as has been pointed out by 

 Friedlaender, that the line wliich has been drawn between the nerve 

 fibres of vertebrates and invertebrates cannot be maintained. 



2. Confirmation for Maldanidaj of the theory that Leydig's fibres do 

 not function in any way as an organ of support. They are neither ho- 

 moloiious nor analogous to the chorda dorsalis of vertebrates. 



3. Confirmation of the view that Leydig's fibres result from the union 

 of the direct processes of giant ganglion cells. In Axiothea torquata and 

 Clymene producta these cells appear in the sub-oesophageal ganglion, 

 and are found scattered along the lateral and ventral portions of the 



(Science, Vol. V. No. 1 15, March 12, pp. 423-436). This report contains (pp. 427, 428) 

 an abstract of a paper by Miss F. E. Langdon on " The Peripheral Nervous System 

 of Nereis virens." The writer says : " The spindle-shaped sensory cells described by 

 Retzius as isolated are really grouped into semi-organs, which have a definite dis- 

 tribution over the body. Each organ consists of a fusiform group of cells, whose 

 bodies lie below the epidermis or in its base. The cuticular markings over the 

 organs in the appendages of the body are like those over the sense organs of Lum- 

 bricus. Over the body itself each cuticular marking is concave on the exterior, 

 and the very thick cuticula encloses beneath each marking an ovoid cavity, 

 through which pass the outer ends of the sensory cells. Each sensory cell usually 

 bears several sensory hairs, and these hairs cannot be retracted normally as sup- 

 posed by Retzius." 



There is one noteworthy difference between this description and that which I 

 have given for the epidermal sense organs of the Maldanidae. I have found only a 

 single sensor;/ hair to each sense cell in case of the Maldanidffi studied, whereas 

 Miss Langdon has found that in the case of Nereis each sensory cell usually bears 

 several sensory hairs. We are, however, in agreement as to the grouping of the 

 sensory cells into multicellular organs. 



