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POPULAR SCIENCE REVIEW. 
Although it is only quite lately that these organs have 
attracted any especial attention, their presence in Scopelus and 
other forms was long ago noted by various observers. It was 
in the year 1839 that the Italian naturalist, Cocco, of Messina, 
had his attention directed to them, and he published figures and 
descriptions of the forms which live in the Mediterranean ; ten 
years later a number of the species which possess these struc- 
tures were treated of in the twenty- second volume of that 
monument of industry and research, in which Cuvier and Valen- 
ciennes systematized our knowledge of the group of fishes. 
But the work begun by the two, and carried on after Cuvier’s 
death as far as the twenty- second volume, could not, even with 
its scope, deal in detail with all the parts of every fish ; and 
even had that been possible, the means of investigation which 
were to hand would doubtless have been insufficient for a 
complete and correct understanding of the organization of 
these parts. Modern methods in histology were above all things 
necessary : even in the case of the human eye, we know that much 
of what is now the common property of all students resulted 
from the studies of Max. Schultze in the middle years of the 
seventh decade of this century. He who will turn to the article 
on the eye which appears in Strieker’s Handbook of Histology 
will see how much has been done since the year 1850 ; and we 
have only to compare the first edition of so easily accessible a 
book as Prof. Huxley’s Lessons in Elementary Physiology (1866) 
with the second, which appeared two years later, to recognize 
at once how all our exacter knowledge of these complicated 
nervous structures is due to the improved methods of compara- 
tively recent times. 
Understanding, then, the real position of affairs, it will be 
easily seen that the investigation of the minute structure of 
these eye-like organs offered quite recently an altogether unex- 
plored field of research. With the exception of a short notice 
by Prof. Leuckart in the year 1865, which led to the belief 
that the parts in question were accessory organs of sight, 
nothing seems to have been published with regard to them till 
the year 1879, when Dr. M. Ussow, of the University of St. 
Petersburg, gave to the world an account of his researches. 
These had been undertaken on twelve species, belonging to 
the seven genera, Astronestlies , Stomias, Chauliodus, Scopelus , 
Maurolicus , Gonostoma and Argyropelecus , all of which are 
small, and most of which live in the Mediterranean. He 
pointed out that the organs might be arranged in two series, 
one of which he regarded as forming accessory eyes, and the 
other as special glandular organs, and he insisted on the fact 
that, though they are both arranged in just the same way, the 
two sets are never found in the same fish. 
