A STUDY IN MORPHOLOGY. 113 



together, as rudimentary buds, before the exopodites of the pereiopods and niaxillipeds 

 disappear. 



The third column of Table VI. shows the resemblances to Lucifer and Acetes at 

 this stage. 



In the immature or Mast'ujopus stage (see CLAUS'S ' Ueber einige Schizopoden und 

 niedere Malacostraken, Messinas ' ) the three forms are almost exactly alike, except 

 as far as the generic distinctions are concerned, and the young Seryestes scarcely 

 differs from the young Lucifer except in the absence of a neck, the length of the 

 flagellum of the second antenna, and the presence of rudiments of the fourth and fifth 

 pairs of pereiopods. 



Comparing the whole course of development of the three forms, as far as it is known, 

 we notice that while the larval stages of Seryestes are much more different than those 

 of Acetes from the corresponding stages of Lucifer, the character of the change at 

 each moult is much more like what we have in Lucifer than what we have in Acetes. 



We cannot fail to notice, in the second place, that the attempt to express the facts 

 of the metamorphosis of these forms, so far as we know them, in a tree-like diagram, 

 would result in a tree placed upside down, with the branches which represent the 

 three Protozoeas much more divergent than those which represent the three young 

 Sergestids. A similarity of type runs through the whole metamorphosis, but it is 

 no more marked at the early stages than it is in the late stages, while the secondary 

 differences are much more conspicuous during the Zoea and Aeanthosoma stages 

 than they are as we approach the adult form. 



While this is true it is also true that if we imagine a metamorphosis which 

 shall agree with these three in all their common features, but shall have none of the 

 features which they do not all share, we shall have something much more like the 

 metamorphosis of Lucifer than that of Acetes or Sergestes, and we must therefore 

 regard the life-histories of these three forms as somewhat divergent modifications of a 

 form of development which is at present more closely adhered to by Lucifer than by 

 the other two, and in this metamorphosis we must recognise a Protozoea stage when 

 the two pairs of antennse are locomotor, the ocellus present, the labrum furnished with 

 a spine, the carapace armed with posterior dorsal and lateral spines and a rostrum ; 

 the two pairs of maxillse, and two pairs of maxillipeds present, and the thoracic and 

 abdominal segments without appendages. This stage persists, with slight modifi- 

 cation, through several moults in all of them, and is followed by an Aeanthosoma stage, 

 in which the carapace has a rostrum and antero-lateral spines, and a smooth posterior 

 edge ; the eyes are stalked ; the two pairs of antenna? have their adult character ; 

 there are at least four pairs of pereiopods with swimming exopodites ; the swimmerets 

 are large and have their adult form, and the other abdominal appendages are absent. 

 The duration of this stage and the mode of transition to the next varies in the three 

 forms, but it is followed in all by what may be called a Jfdstigopus stage, characterised 

 by the general features of the family. 



MDCCCLXXXII. y 



