198 report— 1878. 



For the term pupa I believe that Mr. Darwin is mainly responsible. He 

 having introduced it in his monograph on the Cirripedia, when there ap- 

 peared to be a great change in the progressive growth of the young which 

 was thought to equal the metamorphosis of insects, if not to represent it 

 in kind. 



I therefore propose to substitute the term Brephalus (from f3pE<pog f 

 infant : a\c, sea), or young marine animal, for the term larva, while 

 that of " pupa " had better be suppressed. Seeing that the development of 

 the animal is gradually progressive, there is no stage or state of the 

 animal which can be represented by it. 



In this Report, whenever used, the term brephalus will mean the form of 

 the animal as it quits the ovum, no matter whatever stage of develop- 

 ment it may represent. 



The several terms used for the young animal in its separate stages have 

 been taken from animals which had been previously described as adults. 

 These are, Nauplius, Zoa?a, Phylosoma, and Megalopa. Each of which is 

 now recognised as being a stage in which the brephalus quits the ovum, 

 and therefore one in the development of the Crustacea. To these must now 

 be added those of Metanauplius and Protozcaea. 



The term nauplius, as representing one of the stages in which the 

 embryo of the Crustacea quits the ovum, was introduced by Fritz-Miiller 

 in 1864, in consequence of his having taken a small crustacean that 

 while in general form it resembled the entomostracan genus Nauplius, 

 yet exhibited unmistakable evidence of being the young of some macrurous 

 decapod : which he believed to be that of Penceus. 



Metschnikoff has announced that the brephalus of Euphausia is in the 

 form of nauplius, while it is known to be that of all the cirripedes as well 

 as most of the entomostracous Crustacea, but these last, excepting Bran- 

 chipvs, differ from the typical Nauplius in having but two pairs of free 

 appendages. 



The nauplius, as it quits the ovum of the Malacostracous parent, is an 

 animal of an ovate form, having three pairs of free appendages, the first 

 of which is unibranched while the other two are biramose, and a single 

 ophthalmic spot or imperfect central eye, and a strongly projecting 

 labrum or anterior lip. 



This is the state in which Euphausia (Plate V., fig. 4) is hatched accord- 

 ing to Metschnikoff ; and Pena?us according to Fritz-Miiller. (PI. V., 

 fig. 1.) 



Shortly after it has become a free swimming animal it moults its 

 external skin, and with each successive exuviation it advances a stage in 

 development, its first apparent advance is in the appearance of lobes that 

 ultimately become the appendages of the mouth. Metschnikoff remarks 

 that this phenomenon is common to the nauplius of Euphausia and Penceus, 

 that is, the contemporaneous formation of several appendages succeeding 

 the three original pairs of swimming feet. 



He says moreover that it is remarkable that such a mode of formation 

 is not observed in any of the Entomostraca which have been developed 

 through the nauplius metamorphosis. 



It is this stage for which Clans has suggested the tercn Metanauplius 

 (PI. V., fig. 2), while that for which he proposes the name of Protozowa 

 is when the pleon is developed, but neither the pereiopoda or appendages 

 of the pleon are present. (PI. V., fig. 3.) 



But here we have so close an approximation to the Zoaea as it leaves the 



