114 MR. W. K. BROOKS ON LUCIFER: 



In all three forms the somites, and with the exception of the swimmerets the 

 appendages also, develop in serial order from in front backwards. 



The interesting question whether we are to attribute to this typical form of develop- 

 ment a fifth thoracic somite and appendages must, I think, be left in doubt. A 

 comparison of the Sergestid larvae seems to indicate its absence, but wider comparison 

 with Penceus and the Schizopods seems to lead to the opposite view. 



Comparison of Penseus with the Sergcstidce. 



In order to render the comparative tables as complete as possible, I have added 

 columns showing the corresponding stages of Penceus and Euphausia. 



FRITZ MULLER has described a number of stages in the development of a species of 

 Penceus (" Verwandlung der Garneelen," Arch. f. Naturgeschichte, 1863, pp. 8-23, 

 taf. ii.). The series commences with a Nauplius which may belong to the same species, 

 although we have no certainty of this. In a second paper (" Ueber die Naupliusbrut 

 der Garneelen," Zeit. f. Wiss. ZooL, xxx., 163-166) he gives, in reply to doubts which 

 had been expressed to him by SPENOE BATE, ALEX. AGASSIZ, PAUL MAYER, and 

 others, the following reasons for believing in the specific identity of all the forms in 

 his series : 1st, the peculiar mode of locomotion ; 2nd, the resemblance in colour ; 

 3rd, the great length of both pairs of antennae ; 4th, the character of the mandible ; 

 5th, the presence of four pairs of buds in the Nauplius, and four corresponding pairs 

 of limbs in the Zoea ; 6th, the similarity in the structure of the heart, digestive tract, 

 and liver in the Nauplius and the youngest Zoea ; 7th, the presence of frontal organs 

 in both stages. As all the points except the colour would apply to any Crustacean 

 which passes through a Protozoea stage, there is certainly nothing more than a pre- 

 sumption that the whole of his series represents a single species ; but as there is no 

 doubt that the Nauplius belongs to Penceus or to some closely -related form, I have 

 included it in the table. 



FR. MULLER'S account of the later stages is supplemented by a few additional 

 observations of other species by GLAUS (" Untersuchungen," &c., pp. 11 and 41, taf. ii. 

 and iii.), and I have compiled the columns in the tables from both sources. 



The first Nauplius stage (Table II., column 3) appears to be more simple than that 

 of Lucifer, as MULLER failed to observe any buds to represent appendages posterior to 

 the mandibles. 



The Nauplius stage is followed by a meia^-NaupUiis stage (Table III., column 2), 

 which is distinguished from that of Lucifer by the great size of the blade of the 

 mandible, by the presence of frontal organs, and by the shortness of the carapace. 



The next stage is a Protozoea (Table IV., column 5), with a rounded carapace 

 without spines or rostrum, four basal rings and six terminal joints in the endopodite 

 of the second antenna, a spine on the labrum, two pairs of maxilke, two pairs of 

 maxillipeds, and a long hind body which, according to GLAUS, is divided into six 



