No. 3. — CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY 

 OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD 

 COLLEGE, UNDER THE DIRECTION OF E. L. MARK, No. 163. 



The Optic Rejlex Aj^paratus of Vcrtehrates for Short-circuit 

 Transmission of Motor Beflexes through lieissner's Fibre ; its 

 Morphologu, Ontogeny, Phylogeny, and Function. — Pakt I. 

 The Fish-like Vcrtehrates. 



By Pouter Edward Sargent. 



TABLE OF CONTENTS. 



Introduction 1:^1 



I. Morphological 132 



A. General historical survey . . 132 



1. Reissner's fibre 132 



2. The mesenceplialic nidulus 



of optic reflex cells . . . 136 



B. Methods and material . . . 137 



C. The brain ventricles and cen- 



tral canal and their contents 139 



I. The encephalic cavities . . 139 



1. The cerebro-spinal fluid . 139 



2. Cilia 141 



3. Ependyraal groove . . . 141 



4. Sense organs 142 



II. Contained material . . . 142 



1. Coagulum 142 



2. Epithelial cells .... 143 



3. Blood corpuscles .... 143 



4. Artifacts 143 



5. The posterior canal cells . 144 



6. Reissner's fibre .... 144 

 a. Appearance in the fresh 



condition 144 



h. Appearance in sections . 144 



c. Internal structure . . 145 



d. Size 146 



D. Morphology and ontogeny of 



Reissner's fibre and its cellu- 

 lar connections 148 



I. Cyclostomcs 148 



A. Historical 148 



VOL. XI.V. — NO. 3 



