1881.] 



Lucifer : a Study in Morphology. 



47 



and its inner granular end, which is now situated in the segmentation 

 cavity, soon divides up into a number of food-yolk spherules. 



The primitive digestive cavity is next formed by an invagination, 

 at the point where the yolk-pyramid has been pushed in. 



The larva leaves the egg as a Nauplius, which, after two moults, is 

 changed into a Protozocea, with nauplius-like antennules and antennae ; 

 mandibles like those of the adult ; two pairs of maxillae ; two pairs of 

 maxillipeds, and a long hind-body divided at its anterior end into four 

 zoonites. 



After a number of moults it becomes changed into Dana's Erich- 

 thina demissa, which Willemoes-Suhm has shown to be a Lucifer 

 larva. 



The Erichthina gradually changes by three moults into Dana's 

 Serbatina armata, which seems to be the same as Willemoes-Suhm's 

 Ampliion stage. 



After a number of moults it becomes a Mastigopus, and then both 

 sexes gradually assume the adult female form, the characteristics of 

 the adult male appearing last. 



The first four sections of the paper describe the structure, embryo- 

 logy, and metamorphosis of Lucifer. Among the more important 

 points are the total absence at all stages of the fifth thoracic zoonite 

 and its appendages ; the origin of the metastoma as a pair of buds 

 homologous with the other appendages, and the absence of larval 

 stages with the distinctive features of the Elaphocaris and Acanthozooea 

 larvae of Sergestes. 



The fifth section gives an account of the metamorphosis of another 

 Sergestid, which there is reason to believe to be Acetes, although it 

 was not reared to the adult form. At the Elaphocaris and Acanthozooea, 

 stages this form is intermediate between the highly modified larva of 

 Sergestes and the simple larva of Lucifer. 



The sixth section discusses the relation between the larvae of Lucifer, 

 Acetes, Sergestes, Penceus, and Euphausia, and the significance of the 

 deapod Zocea and crustacean Nauplius. 



As one result of the comparison, I attempt to show that, while the 

 Hfe-history of Lucifer, Acetes, Sergestes, and Pendens, tends to confirm 

 Claus' view that the Zoma is a secondary modification of the more 

 primitive Protozocea, a comparison of these forms with Euphausia 

 shows that this view is not without difficulties, since these genera 

 differ from each other in the very point in question ; the manner 

 in which the zoonites and appendages of the thorax make their 

 appearance. 



The seventh section discusses the phenomena of serial homology 

 and bilateral symmetry in the Crustacea, and is an attempt to show 

 that these resemblances cannot be explained by heredity from the 

 parts of an unspecialised form, since the facts of embryology do not 



