186 KEFERSTEIN, ON SAGITTA. 
connection with the brain which can be perceived within 
the head. But what significance should be ascribed to this 
ventral saddle, I am not able to say; and one looks in vain 
for any hint with reference thereto from the development of 
Sagitta as observed by Gegenbaur. 
Eyes.—The two eyes, as is known, are placed in the in- 
tegument on special rounded ganglia, which, by means of a 
nervous filament, are brought into connection with the 
cerebral ganglion lying in front of them. The eyes consist 
of a quadrangular mass of pigment, which probably conceals 
a retina within, and, externally, supports on either side about 
four or five small, oval, brilliant, crystalline cones; on the 
lateral aspect of the pigment spots, however, the crystalline 
cones are wanting, or, at least, are reduced to two smaller 
ones in front and posteriorly. I have not observed the 
contour which Wilms remarked on this outer side of the 
pigment spot, and was inclined to regard as a cornea or lens; 
and to me, with Leydig, it appears probable that the struc- 
ture of the eye of Sagittta approximates, on the whole, to 
that of the Arthropoda—perhaps of the Daphnide. 
A few figures accompany the original paper. It will be 
remembered that our volume for 1856 contained a full 
abstract of what was then known of the structure of Sagitta, 
together with references to the works of other writers.* 
This was followed, in 1859, by a translation of Gegenbaur’s 
‘Memoir’ on the development of the same organism. More 
recently, Gegenbaur (‘Grundziige der vergleichenden Ana- 
tomie,’ 1859, p. 188) has reiterated his former views concern- 
ing the systematic position of Sagitta, by founding for its 
reception a distinct class, OnsteLMINTHES, between the Ne- 
matotdea and Annelida. 
* To the list there given add Gervais (‘ Ann. ;Frang. et étrang.,’ 1838, 
p. 127); Gersted (* Vedens. Med.,’ 1849, p. 26) ; J. Muller (‘ Archiv,’ 1847, 
p. 158) ; Gosse (‘Tenby,’ 1856, p. 175); and Leydig (‘Lehrbuch der His- 
tologie,’ 1857, p. 261). 
