TRANSITIONAL FORMS 103 
narrowed at its summit, where it is articulated with the 
next joint, and from the latter by the well-formed orbits 
and the entire absence of rudimentary fifth legs.’ Those 
who are always sceptically inquiring for links in the chain 
of evolution and for the fine gradations which the trans- 
mutation of species postulates, may be invited to observe 
in this family the genus Pinnixa, White, in which the 
fifth legs are often short, the genus Amorphdpus, in which 
they are rudimentary, and lastly T’haumastoplax and Hexa- 
pus, from which they have vanished altogether. 
Some curious facts relating to the organs of vision 
in certain members of this tribe are wortby of mention. 
In the family Ocypodide the genus Bathyplax, A. Milne- 
Edwards, 1880, contains but a single species. Specimens 
taken by the U.S.S. Blake from depths between four and 
five hundred fathoms were found to have the eye-stalks 
very short, almost immovable, and with the cornez not 
developed. Accordingly the species was named typhlus, 
‘the blind.’ But specimens taken from smaller depths 
by the Challenger agreed with the others in all respects 
except just this one, that they possessed small, distinct, 
terminal corneee. As these specimens were obviously not 
blind, Mr. Miers named them ‘ var. oculiferus.’ In regard 
to another genus, also but more doubtfully included in 
the Ocypodidz, Professor Perrier cites the observation of 
A. Milne-Edwards, that in Geryon tridens, Kroyer, a 
species which descends to great depths, the eyes are 
brilliantly luminous. 
