A STUDY IN MORPHOLOGY. 
91 
If we neglect the features which, at the end of each stage, make their appearance 
as preparation for the next, we may describe each stage as follows : - 
The Nauplius has three pairs of locomotor appendages, the first antennae, the second 
antennae, and the mandibles; and there is a large labrum without a spine, and the 
carapace and telson are absent. There is an ocellus, but no compound eyes. 
The Protozoea has two pairs of antennae, which are like those of the Nauplius. The 
mandible is reduced to a cutting blade. There are two pairs of biramous maxillae, 
with scaphognathites, and two pairs of biramous maxillipeds. There is a long hind 
body, ending in a flat telson. The labrum has a spine. The carapace is large, and 
has a rostrum, a median dorsal and two lateral posterior spines; and its free edges 
reach down beyond the basal joints of the appendages. There is an ocellus, but no 
stalked eyes. 
The Schizopod stage is characterized by the great change in the two pairs of 
antennae, which are no longer like those of the Nauplius, but have the characteristics 
of those of the adult. All the mouth parts and four pairs of thoracic limbs are present, 
and all posterior to the first pair of maxillipeds are biramous and locomotor. The 
abdomen has six somites and a movable telson. The swimmerets are present, but the 
other abdominal appendages are not. 
The ocellus persists, but the stalked eyes are also present. The carapace has a 
rostrum and two antero-lateral spines, but those at the posterior edge have disappeared. 
The edges of the carapace do not reach over the basal joints of the thoracic limbs, and 
the body is flattened vertically. The labrum still has a spine. 
The young Lucifer and the adult female have a long flagellum on the first antenna, 
a flagellum and scale on the second; the ear and antennary gland are present; the 
neck is elongated. The fourth pereiopod has disappeared, and the others, as well as 
the maxillipeds, have lost their exopodites. The first pleopod has one terminal branch, 
the next four two branches each; the sixth abdominal somite has a smooth lower 
edge. The telson is straight and the outer end of the exopodite of the swimmeret is 
rounded. 
The adult male has a clasping organ on the first pereiopod, three rami on the second, 
two teeth on the lower edge of the sixth abdominal somite, a square end to the 
exopodite of the swimmeret, and a bent telson. 
It is true that these five stages merge into each other somewhat, and that they are 
complicated by the presence of the rudiments of organs which are be functional at the 
next stage; but after all these secondary modifications are allowed for, it will be seen 
that each stage is sharply and definitely marked, and separated by a pronounced gap 
from the stages before and after. 
The significance of these five stages can be best inquired into after the corresponding 
stages of other Sergestidce have been examined, and I will return to the subject further 
on, in a section on the general relationships of the group. 
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