14 THE VOYAGE OF H.M.S. CHALLENGER. 



that of other Crustaceans which pass through this same larval stage. Since the develop- 

 ment of the Copepoda is supposed to be a highly typical one, and since the comparison 

 of these animals with the higher Crustaceans presents no great difficulties, the aim of the 

 researches has been to homologise parts of the body — and especially the appendages — of 

 the ( Srripedia with those of the Copepoda. In this department the papers of Glaus ' take 

 the first place. His last publication on the subject appeared in 1876, and in it he pro- 

 poses the following homologisation of the appendages : — 



The first pair of appendages of the Nauplius becomes in Cirripedia, as well as in 

 Copepoda, the first antennae. In the Cypris-stage of the Cirripedia these antennae are 

 we II -developed, in the full-grown animal only rudimentary. 



The .second pair of appendages of the Nauplius, which in Copepoda develops into the 

 double- branched second antenna, is east off by the Cirripedia, 



The third pair of appendages (loc. cit., p. 76) in Copepoda changes into the mandibles, 

 and in the development of the Cirripedia is cast off like the second pair (according to 

 Metschnikoff," and v. Willemoes Suhm). 3 According to Claus, it becomes the mandible. 

 If the latter suggestion be right — but it is only supposed and has not been actually 

 observed by Claus — the mandibles of both orders of Crustaceans are homologous. 



Behind the third pair, a fourth pair of appendages has appeared. This pair, in the 

 development of the Copepoda, becomes the maxillae ; in the advanced Nauplius-stage of the 

 Cirripedia a double pair of knobs make their appearance in the same place; from the outside 

 one, according to Claus, the maxillae may develop, while the other one evidently produces the 

 second maxilla (inner maxilla, Darwin). According to Metschnikoff, the mandibles and 

 the maxillae of the Cirripedia are together developed from this fourth pair of outgrowths. 

 As to the following pairs of appendages, the Copepoda will be spoken of first: a fifth 

 pair of appendages has made its appearance behind the fourth; these are the maxillipeds, 

 which, though double-branched, represent only one pair of limbs. Behind the maxil- 

 lipeds are two new pairs of double-branched outgrowths ; these eventually become the 

 first two pairs of thoracic appendages (paddles, rowing-feet). The fourth and fifth 

 pair of appendages belong to that part of the body, according to Claus, 4 which is 

 covered by the cephalic shield ; this seems to prove that he considers the sixth and seventh 

 pair as not being placed under this shield, a suggestion which is, moreover, in accordance 

 with his figure 4 on pi. xix. Neither is the carapace of the full-grown animal truly 

 cephalic, since it also covers the first somite of the thorax ; four distinct thoracic 

 somites, each furnished with a pair of appendages, succeed the carapace, and behind this 



1 Claus, C, Die morphologischen Beziehungen'der Copepoden, Phyllopoden, Cirripedien, &c, Wiirzburyer Naturwt. 

 Zeitschr., iii. 1862 ; Die Cypris-ahnliche Larve der Cirripedien mid ihre Verwandlung, Schrift. der Ges. zur Befiird. d. gesamtnt. 

 Natunv., 1869; Untersuchungeu zur Erforschung der genealogischen Grundlage des Crustaceen- Systems, Wien, 1876. 



a Sitzungsb. der Versamml. deutsch. Natwrf. zu Hannover, 1865, p. 218. 



8 Willemoes Suhm, R. von, On the development of Lepas fascioularis, Phil. Trans., clxvi., 1875. 



* Untersuchungen, &c, p. 75. 



