234 
PALEONTOLOGY: R. RUEDEMANN 
ventrally, appears throughout the entire length, to a condition where 
only the occasional presence of a few degenerating cells indicates the 
location of the atrophied duct. 
Increased activity of a single kidney also has a definite effect on the 
segmental duct of that side. Cross sections of the duct of an individual 
with unilateral operation, when compared with either of the ducts of a 
normal larva of the same stage, show a marked increase in diameter. 
The mesonephroi of both sides develop normally, at least in the early 
stages, even after excision of one pronephros. Non-development of the 
segmental duct in one instance left the mesonephric tubules discon- 
nected on that side, and with no outlet for excretory products. No 
specimens have yet been kept a sufhcient length of time to determine 
the ultimate outcome of this abnormal condition. 
In brief then, the following conclusions may be drawn. 
1. Removal of both pronephroi in Amblystoma larvae induces condi- 
tions leading to oedema and subsequent death, though the presence of 
one head kidney is sufficient to keep the embryo in a condition of health. 
2. Excision of one head kidney brings about an increase in size in the 
remaining organ, and also in the diameter of the segmental duct on that 
side. 
3. Removal of one pronephros has no essential effect on the develop- 
ment of the pronephric glomerulus of that side, but the segmental duct 
appears in var5dng stages of atrophy. 
4. Anterior and posterior nephrostomes may regenerate from the 
coelomic epithehum. 
5. Early developmental stages of the mesonephros are normal, even 
after excision of one head kidney. 
ON THE PRESENCE OF A MEDIAN EYE IN TRILOBITES 
By Rudolph Ruedemann 
NEW YORK STATE MUSEUM, ALBANY 
Received by the Academy, March 7, 1916 
The entirely extinct sub-class Trilobita of the Crustaceans, compris- 
ing about 1840 species divided into some 185 genera, has always held a 
central place in the phylogenetic history of all classes of Crustacea. It 
is becoming not only more probable that the Ostracoda and Cirripedia 
were developed from the trilobites, but that also the insect subphylum 
has taken its origin from this ancient class of arthropods. Some authors 
derive the Xiphosura and Eurypterida and through them the scorpions 
and all later arachnidians from the trilobites, and others again, as Patten, 
