HO ME. W. K. BROOKS ON LUCIFER: 



If we assume the correctness of the extremely probable assumption that DOHRN'S 

 and CLAUS'S unknown larva is the earliest Protozoca of Acetes, the resemblances 

 between it and the corresponding larva of Lucifer (compare fig. 27 with GLAUS, fig. 2, 

 taf. iv.) are much greater than they are at a later stage. The chief differences are the 

 presence in Acetes of rudimentary compound eyes ; the great length of the carapace ; 

 the absence of a rostrum and spines ; the great number of joints in the first and second 

 antenna, and the difference in the length of these two appendages ; the deep notch in 

 the telson. The close similarity between the two larvae at this stage will be seen by 

 comparing column 1 of Table IV. with column 2. 



After the moult which ends the Zoea series the differences between the Acetes 

 larva (fig. 89) and the Lucifer larva (fig. 53) become much greater, although they do 

 not obscure the fundamental similarity between the two forms. In each of them the 

 carapace makes less than one-third the total length of the body, and it has a rostrum 

 and two antero -lateral, but no postero-lateral or dorsal spines. The first antenna has 

 lost its swimming hairs, and has developed one flagellum in each form and two in 

 Acetes. In both forms a series of long plumose hairs has appeared on the inner edge 

 of the shaft of the appendage. In both forms the second antenna has lost its 

 locomotor function and assumed the adult form, but it is rudimentary in Lucifer and 

 well developed in Acetes. 



The ocellus is present and the eye stalked and movable in both. 



The fifth thoracic somite and its appendages are entirely wanting in both forms. 

 ' The fourth is biramous in Lucifer, and similar to the ones before it, but in Acetes the 

 limb proper has disappeared and the appendage is represented only by an exopodite. 

 The second and third pairs of maxillipeds, and the first, second, and third pairs of 

 pereiopods are essentially alike in structure in both forms, but in Acetes the endo- 

 podites are rudimentary, covered by a cuticle, and functionless. The swimmerets are 

 present and very similar in the two forms, but the other abdominal appendages are 

 absent in Lucifer, while the first, second, and third pairs are developed, but rudimen- 

 tary in Acetes. The abdominal somites have acquired ventral spines in both forms, but 

 these are very small in Lucifer and long and prominent in Acetes. The telson is long 

 and narrow in Lucifer and short and wide in Acetes. The relation between the two 

 forms at this stage of development will be seen by a comparison of columns 1 and 2 of 

 Table VI. 



The later history of the two genera can hai'dly be divided into parallel stages. 

 Lucifer keeps all its Schizopod limbs for at least two more moults, and as shown in. 

 fig. 54, acquires the rudiments of all the abdominal feet at one time, and before the 

 fourth pair of thoracic limbs and the exopodites of the others and of the maxillipeds dis- 

 appear, while Acetes (fig. 85) loses its exopodites at once, and the maxillipeds, thoracic 

 limbs, and antennae become like those of an adult Sergestid some time before the appear- 

 ance of the five pairs of pleopods ; and these do not appear together, but in two sets. 



It is interesting to note that although the changes which the two forms undergo 



