REPORT ON THE PHYLLOCARIDA. 33 



is here only the antennulse which are peculiarly modified, as is also the case in the 

 Copepoda. 



Homology of the Oral Parts. — These appendages appear on the whole very dissimilar 

 to those in other Branchiopoda, and their structure has consequently been adduced to 

 show the closer affinity of Nehalia to the Podophthalmia. Especially is the great 

 development of the mandibular palp certainly a very characteristic feature, since such a 

 palp is never met with in any adult Branchiopod. In form this palp, however, exhibits, 

 as has also been pointed out by Professor Claus, a much closer resemblance to that in 

 the Amphipoda than to the palp in the Podophthalmia, and the structure of the 

 mandible itself is also rather different, showing, by the reduction of the cutting edge and 

 the great development of the molar surface, more similarity to that met with in the 

 greater part of the Branchiopoda. In the (Copepoda the mandibles are, as is well known, 

 in most cases provided with a well-developed palp, but this palp is generally biramose 

 or Ijears a so-called branchial appendage, which however is often very reduced in size 

 and in some forms even quite obsolete, whereby the palp acquires a certain similarity to 

 the mandibular palp in the Nebaliidas. The very slight development of the posterior lip 

 or metastoma in the Nelmliidae is a character apparently more in accordance with the 

 Entomostraca than with the Malacostraca, in which latter this part is always well 

 developed and rather large. As to the structure of the masillee, both pairs seem to me 

 to be essentially different from those in the higher Crustacea, and especially is the 

 structure of the first pair quite peculiar and only admits of a very general comparison 

 with those in other Crustacea. In the structure of the second pair I find, however, a 

 well-marked resemblance to the maxillse in a great number of Copepoda, and this 

 resemblance is especially very striking in the case of the genus Nehulio-psis, as stated 

 above. In the Copepoda, it is true, only a single pair of maxilla? are present, but this 

 pair I think may more properly be regarded as homologous with the second pair in the 

 Nebaliida3, the first pair not being developed in the former Crustacea. The number of 

 maxillse in the Nebaliida3 cannot be adduced as showing their affinity to the Macacostraca, 

 since we find at least in all Phyllopoda both pairs distinctly developed, though of a 

 rather simple structure. 



Homology of the Branchial Legs. — These limbs, in my opinion, undoubtedly stamp 

 the Nebaliidse as true Branchiopoda, agreeing, as they do, both in structure and function 

 with the so-called branchial feet in other forms of this order. This has, however, been 

 partly combated by some naturalists, who regard them as more closely agreeing with 

 the thoracic legs in the Schizopoda; and, in fact, if we had confined our examination to 

 the structure of these limbs in the altove described genus Paranehalia, such a view 

 might perhaps to a certain extent be advocated, as in this form they certainly exhibit an 

 appearance somewhat approaching that of the legs in the Euphausiida3. On the other 

 hand, I think, that no one will find any trace of similarity between the simple lameUi- 



(ZOOL. CHALL. ESP. TART LVI. — 1887.) Kkk 5 



