240 BULLETIN OF THE 
organs (ocelli) are rudimentary and destitute of pigment (Colossendeis 
colossea, C. macerrima, Sceorhynchus) or entirely absent (Colossendeis 
angusta). On the other hand, in Pallenopsis the ocelli are relatively of 
unusually great size. All the other species are known to occur also in 
shallower water, and the ocelli are of the ordinary form. 
Scaorhynchus and Colossendeis are of especial interest as showing 
clearly from anatomical evidence the complete independence of tho 
accessory legs and first pair of ambulatory legs, which has been already 
proved by Dohrn from embryological data. The accessory legs have 
been something of a stumbling-block in the way of those who would 
trace the Arachnid affinities of the Pycnogonida by a direct homology of 
their appendages. In order to reduce the Pycnogonid appendages to a 
convenient number for such homologizing, the accessory legs have by 
certain writers been assumed off-hand to be simply branches of the first 
pair of ambulatory legs, with which they are usually closely united. 
Dohrn showed that in the early stages there was every reason to 
believe that the two appendages were innervated by entirely distinct 
ganglia, and therefore belonged to different segments of the body. And 
in some adult forms the first ventral ganglion, which supplies nerves to 
the palpi, accessory legs, and first ambulatory legs, is divided into an 
anterior part supplying the two former appendages, and a posterior part 
sending nerves to the latter pair of appendages. In Nymphon, and 
perhaps in some other forms, these two portions are quite separate as 
two independent ganglia, although remaining in close proximity. In 
Sceorhynchus they are separated by a considerable interval, and con- 
nected by slender commissures. These two ganglia are nearly as large 
as the other ventral ganglia, so that there seems to be one more than 
the usual number. Moreover, the accessory legs are separated by a 
wide interval from the ambulatory legs, and are articulated to promi- 
nent lateral processes from the body, scarcely distinguishable, except in 
size, from those to which the ambulatory legs are attached. It is clear 
from this case that this pair of appendages has nothing to do with the 
ambulatory legs, but really belongs to another segment. In Colossendeis 
the aecessory legs have undergone still another and very remarkable 
change of position. They have moved forwards and become so closely 
united to the palpi that the two appear precisely like the outer and in- 
ner rami of a single appendage. As in the case of Scworhynchus, the gan- 
glion from which they derive their nerves is entirely distinct from that of 
the first ambulatory legs, the two being connected by long commissures. 
In all cases, however, the palpi and accessory legs are innervated by 
