A STUDY IN MORPHOLOGY. 77 



In the case of Lucifer the actual increase in size is not very great, but the carapace 

 becomes folded out over the body, and the thick posterior portion of the body of the 

 Nauplius becomes pulled out into the long free movable hind body of the Protozoea,, so 

 that the length is more than doubled, while the vertical thickness of the body is 

 correspondingly reduced. The shape of the larva when seen from ' one side will 

 be understood by a reference to Plate 4, fig. 35, for although this figure was drawn 

 from an older larva, it correctly represents a side view of fig. 27 in all essentials. 



The most marked differences between the meta-NaupUus of Lucifer and the Protozoea 

 are due to the development of the carapace and the hind body. The carapace 

 (fig. 27) is horse-shoe shaped, with smooth lateral and posterior edges, and it forms 

 about one-half of the total length of the body. On the median line of the anterior 

 edge it is drawn out into a long rostrum (R), at the base of which are the cerebral 

 ganglia (yet) and the ocellus (Or). On the median line of the posterior edge of 

 the dorsal surface there is a shorter dorsal spine (ds), and at the outer angles of 

 the posterior edge a pair of lateral spines (Is), which are a little longer than the dorsal 

 one. The side view (fig. 35) shows that the sides of the carapace have folded 

 down on to the sides of the body, and all the appendages, except the antennas, 

 are almost completely covered by it. The appendages are so nearly alike in this and 

 the next stage that it will be most convenient to describe them together. 



The stomach (s) is now divided into a pair of anterior or cephalic, and a pair 

 of posterior or hepatic lobes, and between the cephalic lobes a number of muscular 

 fibres run upwards and forwards from the oesophagus to be attached (at m) to the 

 carapace. The intestine is small and straight (i), but it is not of uniform character, 

 and is divided into a series of small enlargements separated from each other by 

 constricted portions. 



The last of these enlai-gements is much more constant than the others, and its walls 

 are attached to the integument of the abdomen by a number of small muscles. 



It exhibits regular pulsations, which seem to draw water into and out of the anus 

 (a), which is on the ventral surface of the telson. 



The heart (h) is compact, short, situated near the posterior edge of the carapace, 

 and it gives rise to a single median and two lateral anterior arteries. 



The hind body is about as long as the carapace, and it is divided into four somites 

 and a long unsegrnented region (al>d). The study of the appendages shows that the 

 four somites are those which carry the third pair of maxillipeds (Mp. 3), and the first, 

 second, and third thoracic somites ( T 1 , T 2, and T 3). There are no traces of appendages 

 on any of them. The end of the unsegmented region of the hind body forms a well- 

 marked flattened telson (J 1 ), which is slightly notched on the median line, and carries 

 four pairs of stout spines, and one pair of very small ones. The small ones are nearest 

 the median line ; the third pair are the longest and largest, and the fifth pair spring 

 from the edges of the telson, some distance from the end. 



