150 



Part III. — Ticenty-first An7iual Beport 



The epipodite is small and has no filaments. 



1. (Fig. 71.) The appendage is now more specialised. The proto- 

 podite joints are no longer distinct, but fused. 

 The epipodite is still small and without filaments. 

 The branchia shows a little segmentation. 



The 5-jointed endopodite retains the character of the preceding 

 stage, but its first and second joints have now a number of ciliated hairs. 

 Enlarged drawings of two of the spines on the fourth and fifth joints 

 are shown in Figs. 75 and 87. 



The exopodite is of three segments. The first is broader and bears 

 on its outer edge an expanded plate-like ridge, the edge of which has a 

 series of teeth. On its proximal part there are two short plumose 

 hairs. Distal to these there are five curved teeth, three of which have 

 little lateral teeth, while the remaining two are plain (Fig. 71,a). 

 Opposite the upper part of the ridge there are two similar teeth. The 

 third joint bears five plumose setse and a plain hair. 



Third Maxillipede and Pereiopods. 



The third maxillipede and the five pereiopods are not functional in 

 the Zoea stages ; they are found in the I. Zoea as buds, forming with 

 the diminutive sternum region pertaining to them a hemispherical mass 

 situated between the bases of the second pair of maxillipedes and the 

 first abdominal segment. The mass lies as it were in a cup-shaped 

 depression. It is seen in side view in Fig. 76, and in ventral 

 view in Fig. 85. The sternal region is an oval plate or disc, and is 

 surrounded on both sides by the closely-packed buds of the third 

 maxillipedes and pereiopods. The sternum shows some indication of 

 segmentation. 



The buds of the third maxillipede and pereiopods were shortly 

 described by Spence Bate as follows (;?. : — " Posterior to the last pair 

 of members that I have described [maxillipedes], several sacs are visible. 

 These evidently contain the germs of the five pairs of pereiopoda, or 

 true ambulating legs, the most anterior of which I think I have been 

 enabled to perceive lying folded within the sac, as shown in Plate XL., 

 Fig. 10. Some of the small sac-buds probably are the germs of the 

 future branchiae, and it is not improbable that in the embryonic condition 

 they fulfil the object of their design sufl&ciently well for so immature a 

 creature."* That respiration is carried on by the buds of the gills 

 is not at all likely. 



In tracing the development of the branchij?; it will be shown that, 

 during the present research, conditions were observed partly in agree- 

 ment with the view expressed by Hansen regarding the connection 

 between the limbs and the branchiae. According to that author, the 

 explanation of " the fact that in the Decapods branchiae are found upon 

 the pleurae, upon the arthrodial membrane between the pleurae and the 

 limb, and also upon the coxopodite," is to be found in the view that 

 *' the portion of the pleurae provided with branchiae is to be regarded as 

 originally belonging to the limb, so that we now find its vanished 

 segment represented by branchiae alone." 



Third Maxillipede, 3mp, Plates ix. and x. 



I. (Figs. 69, 76, and 85). The third maxillipede is a bifid bud ; the 

 branches are of unequal breadth; the narrower is the exopodite. On the 

 outer surface there are two swellings ; the smaller, which is distal, is the 



'"■ Op, cit. 



