REPORT ON THE PHYLLOCARIDA. 35 



Thus, the pleopoda in the Nebaliidfe undoubtedly agree very closely with the swimming 

 legs in the Copepoda both as to structure and numlier, whereas their affinity to the 

 pleopoda in the Malacostraca is much more remote. To compare them to the caudal 

 limbs or the so-called saltatory legs in the Amphipoda, as proposed by Professor Claus, is, 

 I think, objectionable, since the latter limbs belong to a ditFerent division of the body 

 and more properly answer to the rudimentary caudal limbs in Nehalia. As to the mode 

 in which the pleopoda are moved, we find also the greatest resemblance between Nehalia 

 and the Copepoda, especially those of the Harpactoid group, the movements being not at 

 all rhythmical nor performed in the same rapid and almost vibratile manner as in the 

 Amphijjoda and most Podophthalmia (Euphausiidse). The two rudimentary caudal limbs 

 in the Nebaliidae likewise find their homologues in the Copepoda. The first of these pairs 

 are thus evidently homologous with the generally very small and imperfectly developed 

 so-called last thoracic legs in the latter Crustacea, and on closer examination we shall find 

 that also the second pair of these limlis are represented in the Copepoda, though in a 

 very rudimentary state. Thus, on the segment succeeding the so-called last thoracic 

 segment in the latter Crustacea, and generally described as the first abdominal segment, 

 there occur in most of the forms on each side, close to the genital orifice, a small tubercle 

 provided with a few spine-like bristles. This tubercle, more distinct in the males, is 

 undoubtedly the rudiment of a pair of limbs, evidently answering to the second pair of 

 rudimentary caudal limbs in the Nebaliidae. The succeeding segments in the Copepoda 

 as also in the Nebaliidae are entirely devoid of any trace of limbs, and in most of the 

 Harpaetoidea these segments exhibit a denticulate armature on the hinder edge quite 

 similar to that in the Nebaliidae. Finally, the caudal rami appended to the last segment 

 in the Nebaliidae are undoubtedly homologous with the so-called " furca" in the Copepoda, 

 as also with the caudal lamella3 in the Branchipodidae, being not true limbs but more 

 properly representing a bipartite terminal segment. These terminal appendages in the 

 Nebaliidae are therefore not at all homologous with the so-called uropoda in the Mala- 

 costraca, the latter being true ventral limbs. 



Homology of the Internal Organs. — The internal organisation of Nehalia, which I 

 have also thoroughly studied in the northern form Nehalia bipes, may on the whole be 

 said to be much more advanced than in any other of the known Entomostraca, but I do 

 not find in this respect any closer resemblance to that of the Podophthalmia, whereas it 

 exhibits some points of apparent affinity to that met with in the Amphipoda. 



The nervous system seems in fact to differ essentially in structure from that generally 

 met with in the other Branchiopoda by the ganglionic cord being not double but forming 

 a single median series of ganglia, as in most Malacostraca. It must, however, be 

 remembered, that the peculiar double ladder-like ventral cord, though very characteristic 

 of the Branchiopoda, does not form a universal character of these Crustacea. Thus, 

 among the Cladocera we find the nervous system in Leptodora wholly dissimilar from 



