A STUDY IN MORPHOLOGY. 109 



VI. RELATION BETWEEN THE LARV^ OF LUCIFER, ACETES, SERGESTES, PEN.-EUS, 

 AND EUPHAUSIA, AND THE SIGNIFICANCE OF THE DECAPOD ZoEA AND THE 

 CRUSTACEAN NAUPLIUS. 



The general significance of the peculiar type of Decapod metamorphosis, of which 

 Lucifer is now the most thoroughly known illustration, has been discussed with the 

 greatest ability and knowledge of the facts by GLAUS in his ' Untersuchungen zur 

 Erforschung der Genealogischen Grundlage des Crustacean-Systems.' My own ac- 

 quaintance with the phenomena of Crustacean morphology in general is very far from 

 being sufficiently extended and minute to qualify me for a critical discussion of this 

 work ; but while the facts in the life-history of Lucifer seem to tend to a similar con- 

 clusion, and even to place it upon a much firmer basis than before, they also indicate 

 that CLAUS'S views cannot receive unqualified acceptance in their present shape. 



I shall not venture at present upon the broader aspects of the question, but I wish 

 to draw attention to the resemblances and differences between the various larval 

 stages of Lucifer and those of a few closely-related forms. The materials which are at 

 present available for a comparison of this kind are extremely scanty, for there is no 

 other closely-related form in which all stages, from the egg to the adult, have been 

 actually traced in a single species by rearing captive specimens. 



Comparison of Lucifer and Acetes. 



The genus which shows the closest similarity to Lucifer is Acetes, but in this case 

 we are ignorant of both the early and the later stages. During the last "Zoc'a " stage 

 the resemblance between the two forms is well marked, and is shown in such features 

 as the similarity in the shape of the carapace and hind body ; in the length and struc- 

 ture of the two pairs of antennae ; in the mode of locomotion ; by rowing with the 

 antenna3 ; in the presence of an ocellus ; the presence of a spine on the labrum ; the 

 close similarity of the mouth parts and maxillipeds ; the rudimentary structure of 

 the thoracic limbs and swirnmerets ; the total absence of the fifth thoracic somite ; 

 and the absence of the first five pairs of pereiopods. Notwithstanding these resem- 

 blances the differences are quite conspicuous. The eye is sessile in Lucifer, stalked in 

 Acetes. The shaft of the first antenna is one-jointed in Lucifer, two-jointed in Acetes. 

 The endopodite of the second antenna has two basal rings in Lucifer, four in Acetes. 

 The two lobes of the metastoma are conspicuous in Acetes, and could not be made 

 out at ah 1 in Lucifer. The abdominal somites are rounded in Lucifer, and spiny in 

 Acetes; and the telson is deeply forked in the latter, slightly notched in the former. 

 In a word, the resemblances between the two are general rather than detailed, and 

 the differences are specific differences of the same character as those between closely 

 related adult animals. A comparison of column 2 of Table V. with column 1 will 

 show these resemblances and differences in tabular form. 



