200 



INVEETEBRATA 



CHAP. 



become first forked, then jointed, and so the adult form is 

 attained. 



Glaus, in the paper cited, has given an interesting sketch of the 

 differences between Nauplii of different species, and one of the most 

 interesting facts which he brings out is that in the larvae of 

 Cyclopsinidae, in which more yolk is contained in the egg, the 

 masticatory hooks on the second and third appendages are absent, 

 and the animal at first takes no food. 



When we examine the life history of the Phyllopoda, we find 

 that in the Branchiopoda and in one or two cases amongst the 

 Cladocera, the young animal enters on its free-swimming existence 

 as a Nauplius larva. In most Cladocera, however, the whole 

 development is completed within the egg-shell, and the animal 



Fig, 147. — The " Cypris " larva or Pupa of Lepas fascicularis .seen from the side. 

 (After Willemoes-Suhm. ) 



add, adductor muscle of carapace ; a(l, first antenna ; caudj, caudal fork ; ex, excretory organ 

 (shell-gland) ; fix, disc for fixation ; Jix.gl, fixing gland ; gn, gnathites (i.e. mandible, first maxilla, 

 second maxilla) ; int, intestine ; m, month ; lab, lahrum ; oci, simple eye ; oc^, compound eye ; th, 

 thoracic legs. 



hatches out with aU the adult features already developed. The 

 Nauplius larva, when it appears, shows the same general features as 

 the larva of Cyclops, but the upper lip is very long and projects 

 backwards, covering the ventral surface. 



If we turn to the Branchiopoda we find that the NaupHus larva 

 is characterized by the great development of the post-oral portion of 

 the body, and by the fact that the third appendages are not forked 

 (Fig. 146, A). After the first moult, before any more appendages 

 appear, the post-oral region becomes marked by a series of four or 

 five transverse grooves, an indication of as many segments, and in 

 the larva of Apus these are evident when the larva first escapes from 

 the egg-membrane. Just as in the case of Cyclops so in Apus and 

 other genera of Branchiopoda there comes a critical moult, at which 

 antennae and mandibles are reduced to their adult proportions. 



The Cladocera are remarkable for retaining throughout life the 



