1912.] NATURAL SCIENCES OF PHILADELPHIA. 429 



3. On the ventral surface of the head the photophores have 

 evidently a primary arrangement in longitudinal series, but this 

 has become so modified by the interpolation of various shorter 

 series and isolated organs that the exact number of rows is difficult 

 to determine. Most apparent are (a) the usual median row which 

 bifurcates at the apex of the funnel groove and at the base of the 

 ventral arms, along which latter its two branches continue for the 

 proximal two-thirds of their length; (6) a long lateral series beginning 

 on the ventral fold of the olfactory crest which curves inward on 

 the head and also continues out the ventral arms to their extremities; 

 (c) a very distinct circlet of more ovoid organs surrounding the ocular 

 aperture (PL IX, fig. 2). 



4. The ventral arms as just noted have two rows of photophores 

 upon the arm itself, and in addition a distinct row of 7-8 small 

 very distant organs along the outer margin of the keel. The third 

 arms have but a single row of 4-5 organs along their ventral aspect. 

 On the remaining arms, on the tentacles, and on the dorsal surface 

 of the head no luminous organs were observed. 



In addition to the photogenic organs of the general integument 

 and the curious pigmented structures already described at the tips 

 of the ventral arms, there is a third very distinct type of photophore 

 in the form of a series of small circular bead-like bodies, brownish- 

 orange in color, on the ventral periphery of the eyeball; these are 

 five in number, the three central ones smallest and interspaced from 

 one another about a millimeter; the two terminal ones are each distant 

 about 1| mm. from the neighboring organ and their diameter is 

 about twice as great (i.e., rather less than a millimeter) (PL IX, fig. 3). 

 These organs, though situated on the eyeball itself, are usually 

 visible even when the latter is closely retracted, because of a small 

 ovate hyaline non-pigmented area in that portion of the ventral 

 integument which normally covers them. When, as sometimes 

 occurs, this area is iridescent and a little distended, it becomes quite 

 conspicuous. Its purpose is obviously to allow the rays of light 

 from these organs to pass through the outer integument with as 

 little obstruction as possible. 



Color in life not observed; in alcoholic specimens the ground 

 color is a pale brownish-buff, dotted over nearly the entire surface 

 with small and very beautiful reddish-brown chromatophores, 

 which are especially numerous and darkest just above the keel of 

 the gladius, but thickly scattered, even on the ventral surface where 

 they are very conspicuous among the bluish photophores. On 



