404 



GEOLOGICAL SUKVEY OF THE TEKEITORIES, 



The syncerebrum of tlie Tetradecapoda (Amphipoda and Isopoda), 

 judging by Leydig's ftgures^ and our own observations (from dissections 

 made by Mr. J. S. Kingsley) on that of Idotaea and Serolis^, is built on 

 a diiferent plan from that of the Decapoda. The syncerebrum of the 

 Phyllocarida is somewhat like that of the Cladocera and Copepoda (Cal- 

 auidfe) ; being essentially different from that of the majority of the 

 Malacostracous Crustacea. 



The Copepodous syncerebrum is an unstable, highly variable organ, 

 but on the whole belongs to a different category from the syncerebrum 

 of other Neocarida. 



We have then, probably, three types of syncerebra and two types of 

 archicerebra among existing Crustacea. 



HOMOLOGIES OJP THE CRUSTACEAN LIMB, 



Comparison with limbs of Cladocera. — We should naturally first com- 

 pare the appendages of che Phyllopods with the members of their own 



Fig. 27. — First leg of male of Moina (for compariaon with that of male Limnetis) : ex, exite; epip, 

 epipoilal portion of limb; enl^-en^, endites 4-6, to compare witli the endites forming the hand of the 

 male Limnetis. The base of the endopodal region {on 1-3) not differentiated as in the I'hj'llopod limb. 



order, and especially the Cladocera; and here, whether we consider the 

 carapace- valves, the eyes single and compound, the two pairs of antennse, 

 or the telson,. we find a very close connection in form between Limnetis 

 and Daphnia or Moina. In the accompanying figure from Grube's 

 and Weismann's excellent paper on the Daphnidte^ (which we have 

 slightly modified, introducing dots in the branchial portiou) may be 

 seen how nearlj^ the first leg of the male of Moina rectirostris agrees 

 with that of the male Limnetis, as seen in the sixth endite forming 

 a claw like that of Limnetis, although the tiabellum is not clearly dif- 



■ Tafeln znr Vergleicheuden Anatomie. Von F. Leydig. Tubingen, 1864. 



2 Zoology for High Schools and Colleges, figs. 255, 256. 



=5 Ueher einiger neue oder unvollkommen gekannte Daphniden. 1877. 



