CRUSTACEA. 



pendage, which is of value for interpreting the parts of the various 

 malacostracan appendages. They consist (fig. 209) of a basal portion 

 (protopodite of Huxley) bearing two rami. The basal portion has 

 two projections on the inner side. To the outer side of the basal 

 portion there is attached a dorsally directed branchial sack (br) 

 (epipodite of Huxley). The outer ramus (ex) (exopodite of Huxley) 

 is formed of a single plate with marginal setae. The inner one (en) 

 (endopodite of Huxley) is four-jointed, and 

 a process similar to those of the basal joint 

 is given off from the inner side of the three 

 proximal joints. e<T - 



At the third ecdysis several new features 

 appear in the cephalic region, which becomes 

 more prominent in the succeeding stages. 

 In the first place the paired eyes are formed 

 at each side of and behind the unpaired 

 eye, secondly the posterior pair of maxillae 

 is formed though it always remains very FIG. 209. TYPICAL PHYL- 

 rudimentary. The shell gland becomes fully ft P m D cl ^ NI)AGE - (C pied 

 developed opening at the base of the first ^ exopodite; en. endo- 

 pair of maxillae. The dorsal shield gradu- podite; br. branchial appen 

 ally grows backwards till it covers its full da 8 e (epipodite). The basal 

 complement of segments. H? S!fi 



After the fifth ecdysis the Nauplms ap- separated from the endopo- 

 pendages undergo a rapid atrophy. The clite - 

 second pair of antennae especially becomes 



reduced in size, and the mandibular palp the primitive Nauplius 

 portion of the mandible is contracted to a mere rudiment, which 

 eventually completely disappears, while the blade is correspondingly 

 enlarged and also becomes toothed. The adult condition is only 

 gradually attained after a very large number of successive changes of 

 skin. 



The chief point of interest in the above development is the fact 

 of the primitive Nauplius form becoming gradually converted without 

 any special metamorphosis into the adult condition 1 . 



Branchipus like Apus is hatched as a somewhat modified Nauplius, 

 which however differs from that of Apus in the hinder region of the body 

 having no indications of segments. It goes through a very similar meta- 

 morphosis, but is at no period of its metamorphosis provided with a dorsal 

 shield: the second pair of antennae does n >t abort, and in the male is pro- 

 vided with clasping organs, which are perhaps remnants of the embryonic 

 hooks so characteristic of this pair of antennae. 



The larva of Estheria when hatched has a Nauplius form, a large 

 iipper lip, caudal fork and single eye. There are two functional pairs of 



1 Nothing appears to be known with reference to the manner in which it comes 

 about that more than one appendage is borne on each of the segments from the 

 eleventh to the twentieth. An investigation of this point would be of some interest 

 with reference to the meaning of segmentation. 



