72 MR. W. K. BROOKS ON LUCIFER: 



III. GENERAL ACCOUNT OF THE METAMORPHOSIS OF LUCIFER. 



The most instructive method of studying the metamorphosis of Lucifer is to trace 

 each part of the body through the series of changes which it undergoes from its first 

 appearance until it assumes the adult form ; but as this method of comparing the 

 successive stages in the development of each organ necessarily involves references to 

 other organs, it seems best to give first a general account of the whole structure of the 

 larva at each stage of development, and afterwards to go over the same ground more 

 rapidly in a different way, and to trace the history of each appendage. 



The egg Nauplius. 



About thirty hours after oviposition the eye spot and appendages of the Nauplius 

 became visible inside the egg-shell, as shown in a ventral view in Plate 2, fig. 21, 

 and in a dorsal view in fig. 22. If the egg-shell is torn at this stage the embryo 

 escapes, and swims about quite vigorously for a short time, but soon dies. The various 

 parts of the body are much better shown in the swimming embryo than while it is 

 contained in the egg, and I therefore give, for comparison with figs. 21 and 22, a 

 dorsal view (fig. 23) and a ventral view (fig. 24) of an embryo which has thus been 

 set free. 



Fig. 23 shows an embryo of exactly the same age as those in figs. 21 and 22, while 

 fig. 24 was drawn from an embryo a few hours older. The difference in the outline of 

 the body is not due to this difference in age, however, but to a slight change in the 

 point of view. In all four figures the letter e marks the anterior end of the body, and 

 fig. 22 is a view directly opposite to fig. 21. Fig. 23 is in the same position as fig. 22, 

 but the embryo shown in fig. 24 was in such a position that more of the anterior 

 surface and less of the posterior surface was visible than in the other figures. 



On the median line of the ventral surface the labrurn (figs. 21 and 24, L) is very 

 conspicuous at the anterior end of the body, and behind it there is a double row of 

 four pairs of bud-like eminences, arranged in a longitudinal series. The first pair 

 (figs. 21 and 24, //) are much larger than the others, and the depression which separates 

 them on the median line is less marked than it is in the three pairs which lie behind. 

 It is rather difficult to decide with certainty what this pair of buds becomes, but in 

 the larva which METSCHNICKOFF studied the changes were more gradual than they 

 are in Lucifer, and he was therefore able to trace their history more satisfactorily, 

 and to show that they become the rnetastoma. Their position with reference to other 

 parts indicates that they have the same history here, and that the other three pairs of 

 buds are the first and second maxilla? and the first pair of maxillipeds (Mx. 1, MX. 2, 

 and M'p. 1). 



Three pairs of much larger appendages are folded down on to the sides of the body, 

 within the egg ; and when the embryo is set free they are seen to be the first antenna? 



