APPENDAGES AND NERVOUS SYSTEM OF APUS CANCRIFORMIS. 367 
internal ramus (5) of Nebalia’s swimming foot is not the 
same apophysis as that which forms the internal ramus of 
Callianassa’s first maxillipede. For as shown by a com- 
parison of the first maxillipedes of Carcinus (/) and of 
Caridina (JV), an apophysis (number 5) which is already 
much reduced in Caridina has altogether disappeared, both 
in Callianassa and in Pagurus (JZ). 
This simulation of identical constitution by the thoracic 
foot of Nebalia and the maxillipede of Callianassa is an 
example of that ‘pseudomorphism’ which renders the 
determination of homologies of the parts of the Crustacean 
appendage in different regions and in different genera so 
difficuit a problem. 
The first maxillipede of Pagurus (woodcut, fig. 1, JZ) 
presents a feature which is of importance in relation to the 
determination of the parts present in the second maxilla of 
Astacus and allied forms. The second maxilla in the latter 
is destitute of any developed representative of the flabellum 
(epipodite) ; on the other hand, the first maxillipede usually 
in these Decapoda has a well developed flabellum. Pagurus, 
however, presents a first maxillipede, which, like the second 
maxilla of other Decapoda,is without any flabellum, and in 
connection with that absence we find a tendency of the sixth 
endite (exopodite) to become broad and flabelliform, as it is 
in the second maxilla. In Caridina(JV/ ), a very small flabel- 
lum is present on the first maxillipede, and by its presence 
confirms the identification of parts adopted in regard to the 
first maxillipede of Pagurus. 
Tue Centrat Nervous System or Apvus. 
The remarkable condition of the central nervous system 
of Apus has been described and figured with great care by 
Zaddach, but whether his observations have been considered 
untrustworthy, or from whatever cause, no notice has been 
taken by recent writers of the very significant and excep- 
tional disposition of the ganglia in the anterior region of 
the body which he brought to light. There is every reason 
for accepting the accuracy of Zaddach’s observations, not 
only on account of the care which he appears to have given 
to this investigation, but because Grube described in 1853 
(loc. cit.) a very similar but not quite identical disposition 
of the ganglia in Limnetis brachyurus. 
In the Crustacea generally, the two pairs of przoral ap- 
pendages receive their nerves from the preoral ganglion, 
which supplies also the eyes and the integument of the 
