THE EYE-LIKE SPOTS IN FISHES. 
225 
Before proceeding any further with Dr. TJssow’s views, it is 
necessary to state that early in the year 1880 Dr. Gunther gave 
to the Linnean Society an account of these bodies, in which he 
expressed his belief that these organs were producers and not 
receivers of light ; and in his introduction to the Study of 
Fishes, published last year, the ichthyologist just named speaks 
thus in the very last paragraph of his book : ‘ Many pelagic 
and deep-sea fishes are provided with peculiar small round 
organs of a mother-of-pearl colour, distributed in series along 
the side of the body, especially along the abdomen. Some 
zoologists consider these organs as accessorjr eyes, others (and 
it appears to us with better reason) as luminous organs. They 
deserve an accurate microscopic examination made on fresh 
specimens ; and their function should be ascertained from 
observation of the living fishes, especially also with regard to 
the question, whether or not the luminosity (if such be their 
function) is subject to the will of the fish.’ 
One of the required conditions has already been fulfilled. 
Prof. Leydig, of Bonn, has just published a small volume, illus- 
trated by ten octavo plates, in which he deals in great detail 
with what he has been able to observe in the spirit specimens 
of ten species, one of which belongs to a genus (. Ichthyococeus ) 
not examined by Ussow ; to this work we shall shortly return. 
For the moment the prior studies of the Russian naturalist 
claim our attention. 
All, however, agree generally in their account of the arrange- 
ment of these spots ; ordinarily they extend from the pectoral 
fins to the tail, and, according to IIssow, they are covered by 
scales ; sometimes they are found in front of the eye (PL YI. 
fig. 2), on the branchiostegal rays, and on some of the adjoining 
bones ; but these anterior spots never exhibit the same striking 
regularity of arrangement as do those on the abdomen. They 
vary considerably in the number present, but an average is 
found to give the astonishing figure of something like three 
hundred. In Chauliodus Leydig found some thousands of these 
spots. The most simple seem to be found in Astronesthes, a 
genus which did not come under Prof. Leydig’ s examination ; 
these have the form of a biconvex lens, which is strongly swollen 
internally, and has on its outer surface a slight ridge. A layer 
of connective tissue invests the whole of the organ, and is 
clothed internally by a layer of brown pigment cells. At the 
centre of the outer surface there is a small circular orifice, 
from which the deposit of pigment is absent. Just below this 
orifice there is a lens, which is regarded by Dr. TJssow as exactly 
comparable to the crystalline lens of many invertebrate animals ; 
and behind this, and between it and the base of the organ, 
there is a space of some size which is filled with a watery fluid 
NEW SERIES, VOL. V. NO. XIX. Q 
