CRA YF1SH. 291 



several smaller apertures, which admit of entrance but not 

 of exit. 



The blood contains amoeboid cells, and the fluid or 

 plasma includes a respiratory pigment, haemocyanin (bluish 

 when oxidised, colourless when deoxidised), and a lipochrome 

 pigment, called zoonerythrin. Both of these are common 

 in other Crustaceans. 



Respiratory system. Twenty gills vascular outgrowths 

 of the body wall lie on each side of the thorax, sheltered 

 by the flaps of the shield. A current of water from behind 

 forwards is kept up by the activity of the baling portion, 

 or scaphognathite, of the second maxilla. Venous blood 

 enters the gills from the ventral sinus, and purified blood 

 leaves them by the six channels leading to the pericardium. 



Observed superficially, the gills look somewhat like 

 feathers with plump barbs, but their structure is much more 

 complex. The most important fact is that they present a 

 large surface to the purifying water, while both the stem 

 and the filaments which spring from it contain an outer 

 canal continuous with the venous sinus, and an inner canal 

 communicating with the channels which lead back to the 

 pericardium and heart. 



Three sets of gills are distinguishable. To the basal joints of the 

 six appendages, from the second maxillipede to the fourth large limb 

 inclusive, the podobranchs are attached. They come off with the 

 appendages when these are pulled carefully away, and each of them 

 bears, in addition to the feathery portion, a simple lamina or epipodite. 

 The membranes between the basal joints of the appendages ' and the 

 body, from the second maxillipede to the fourth large limb inclusive, 

 bear a second set, the arthrobranchs , which have no epipodites. In 

 connection with the second maxillipede there is a single arthrobranch ; 

 in connection with each of the five following appendages there are two ; 

 so that there are eleven arthrobranchs altogether. There remain three 

 pleurobranchs, one on the epimeron of the fifth large limb, and two 

 others quite rudimentary on the two preceding segments. The bases 

 of the podobranchs bear long setae. 



In Nephrops, the podobranchs are represented by a small rudiment 

 on the second maxillipede, and by five well-developed gills on the next 

 five appendages ; there are eleven arthrobranchs, the most anterior 

 being small ; and there are four large pleurobranchs. 



Excretory system. A kidney or "green gland" lies 

 behind the base of each antenna, and its opening is marked 

 by a conspicuous knob on the basal joint of that appendage 



