90 MR. W. K. BROOKS ON LUCIFER: 



This sexual difference has been pointed out by DOHRN (Zeit. Zool., xxi., 1871, p. 358), 

 but it seems to have escaped the notice of all other observers. 



In the young and in the mature female (fig. 72) the rounded tip projects beyond the 

 tooth (), but as the male approaches maturity the outer edge lengthens, thus pushing 

 the tooth out, as shown in fig. 73, until the end of the appendage becomes square 

 instead of rounded. It is extremely interesting to notice that in Lucifer, as in so 

 many other animals, the adult female is infantile in all the secondary points of 

 difference from the male. 



General view of the metamorphosis of Lucifer. 



A review of the facts which have been described in this section indicates that some 

 of the changes are much more significant than others, since the number of moults is 

 much greater than the number of distinct larval type. 



The meia-NaupUus is obviously a Nauplius with the rudiments of structures which 

 are to appear after the moult, and it must therefore be regarded as a Nauplius 

 prepared for the change into a Protozoca, rather than a distinct stage of development. 



There is no such break between the first Protozoca and the last Zoca as there 

 is between the first Protozoca and the Nauplius. The rudimentary pereiopods and 

 swimmerets of the so-called Zoea are nothing but a preparation for the next stage of 

 development, and the supposed necessity for finding a stage which can be directly 

 compared with the Zoca of the higher Decapods does not justify us in making two 

 larval types out of the unbroken series of Protozoca and Zoca forms. 



It is obvious that the three Schizopod stages are modifications of a single larval 

 type, and the presence of rudimentary pleopods in the second and third stages must 

 be regarded as a preparation for the next stage of development. 



There is no abrupt break between the so-called Mastigopus and the young Lucifer 

 when it is a little older and the neck has appeared. 



On the other hand, there is a real break between the Nauplius and the Protozoca, 

 and the change from one to the other is accompanied by profound structural changes. 

 This is the case also with the transition from the Zoca to the Schizopod stage ; and 

 with that from the Schizopod stage to the young Lucifer stage. The same thing is 

 true to a lesser degree of the change from the immature Lucifer to the adult male. 



The metamorphosis may then be divided into the following well-marked stages, each 

 of which except the last, and in all probability the last also, persists through more 

 than one moult : 



1. A Nauplius stage. 



2. A Protozoea stage. 



3. A Schizopod stage. 



4. An immature Lucifer stage, which persists in the female. 



5. An adult male stage. 



