170 THE RADIATING ORGANS OF THE DEEP SEA FISHES. 



photographs, and drawings were made by Mr. E. Trojan while work- 

 ing in my laboratory. I must express my thanks for the great pains 

 Mr. Trojan has taken with this work ; and for his paper on the structure of 

 the bud-like organs of Malthojjsls spinulosa which I add as an appendix to 

 this memoir. 



Three types of radiating organs are represented by the fishes ex- 

 amined : — ocellar radiating organs, radiating discs, and tubular radiating 

 orscans. 



2. DESCRIPTION OF THE RADIATING ORGANS. 

 (1) THE FISHES WITH OCELLAR RADIATING ORGANS. 

 Argyropelecus lychnus Garmau. 



Plate G, Figs. 34, 35. 



This species has been described by Garman ('09, p. 234, Plate J, Fig. 

 1, lb). The radiating organs are of considerable size, possess exceedingly 

 brilliant reflectors and are surrounded by a layer of dark pigment, so that 

 they are very conspicuous. There are on each side 1 anteorbital (Plate 6, 

 Fig. 25, ao), 1 postorbital (po), 2 opercular (op), 6 branchiostegal (br), 6 

 pectoral (pc), 12 ventrothoracic (vt), 2 anterior lateral (al), 6 medial lateral 

 (ml), 4 ventromedial (ve), 6 anal (a), and 4 ventrocaudal (vc), radiating 

 organs. Besides these there also exists, according to Garman ('99, p. 234), 

 a frontal. 



The axis of all the organs lies very obliquely and nearly parallel to the 

 surface in such a way that it is directed vertically downwards. The anteor- 

 bitals, the postorbitals, and the opercular are simple. The others are joined 

 in longitudinal rows in which they lie side by side. The right and left 

 ventrothoracic organs form a double row which appears as a medial crest, 

 protruding ventrally. All the organs with the exception of the anteorbitals, 

 in which the sheaths are absent, are similar in structure, and size, and the 

 differences in their appearance are due chiefly to the different degrees of 

 coalescence. This is nil in the three cephalic organs mentioned, and greatest 

 in the ventrothoracics. 



The organs are 2 to 3 mm. long and 1 mm. or a little more broad. Each 

 radiating organ (Fig, 24) is composed of a slender elongated ellipsoidal 

 proximal (A), and a narrow funnel-shaped distal part (D). These parts are 



