No. 3. — On Neetonema agile, Verrill. By Henry B. "Wakd. 



I Introduction . . . ■ 



Methods 



II. Systematic .... 



III. Biology 



IV. General Morpliology . 



1. External . . . 



2. Internal . . . 

 V. Anatomy and Histology 



1. Body Wall . . 



a. Cuticula 



a Bristles 

 Scales . 



b. Hypodermis 



a Median Lines 

 c Muscular Layer 

 2 Alimentary Canal 



a. CEsopliagus 



b. Intestine . . 



3. Anterior Chamber 



Con 

 Page 

 135 

 136 

 137 

 139 

 140 

 140 

 143 

 143 

 143 

 143 

 144 

 145 

 140 

 146 

 148 

 151 

 151 

 154 

 156 



TENTS 







Page 





4 



Body Cavity . . . . 



158 





5. 



Nervous System . . 



169 







a. Brain 



159 







a Ganglion Cells . 



159 







/3 Dorsal Cells 



163 







y. Fibrous Mass . 



166 







b Ventral Nerve Cord 



167 







c. Anal Ganglion . . 



169 





6 



Sexual Organs . . . . 



171 







a Male 



171 







b Female 



J 74 



VI. 



Discussion 



177 





1 



Dorsal Cells 



177 





2. 



Large Ganglion Cells . 



180 





3 



Rows of Hairs . . . . 



181 





4. 



Muscular Layer . . . 



181 





5 



Parasitic Nature . . . 



182 



VII 



Comparison with other Forms 



182 



VIII 



Bibl 



iography 



188 



Explanation of Figures 189 



I. Introduction. 



For more than twenty years an interesting pelagic worm has been 

 frequently captured at the ISTewport Marine Laboratory. It was proba- 

 bly first seen by Dr. Alexander Agassiz, who encountered it as early as 

 1870. His first recorded observations, made in 1871, as well as his 

 subsequent studies, have remained, however, in the form of unpublished 

 notes and drawings, which were placed at my disposal in June, 1891, 

 when I began the present study. Two of these drawings, which illus- 

 trate most clearly the external appearance, and show also some of the 

 internal organs, are reproduced on Plate I. Figs. 3, G. 



In 1873 Professor A. E. Verrill published, under the title " (/e7i. indet.,^' 

 a short description of two specimens captured in towing near Wood's 



^ Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology, under the direction of E. L Mark, No. XXXII. 

 VOL. XXIII. — NO 3. 10 



