INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 631 



Ambulatory abdominal legs, from being hairless and immobile, 

 become fully developed at the first change of skin. 



Gills fully developed from the first, 



Post-ahdominal legs begin by having all their ultimate structures, 

 except the hairs and grasping hooks, of which the here specially 

 long appendage of the endopodite of the second pair is the last to bo 

 added. 



Tail has a distinct end-piece, with thirty-two to thirty-four bristles, 

 mostly plumose on both sides : the lateral tail-pieces arc visible in tho 

 interior. At the third stage the feet and outer and inner lateral 

 laminae appear ; at the fourth the inner laminfe are longer and broader, 

 and set round with plumose bristles ; at the fifth and last the median 

 piece becomes pointed, and carries two i^airsof strong spines laterally. 

 The number of its plumose hairs diminishes to eight or nine (subse- 

 quently raised to twenty and upwards). 



The reason of the almost entire absence of the zooea-structures in 

 tho newly-hatched young appears to be due to the, at times, turbu- 

 lent streams inhabited by the species, which are liable to be flushed 

 by torrents ; hence tho zooea and all larval stages, in which a 

 swimming mode of progression exposes them to injury from this 

 cause, are passed through in three or four days, at the end of which 

 time the ambulatory legs with their sharp and strong claws are well 

 developed. 



It is strange that the very closely allied Hippohjte polaris also has 

 a shortened development, while a Brazilian Hippolyfe is known to 

 emerge from the egg as a zooea. 



Toilet-appendages of the Crustacea.* — In tho genus Pahvmon, 

 Dr. Fritz Miiller states, tho first pair of feet is used for the cleansing 

 of tho body and the respiratory chambers. Its structure adapts it 

 admirably for this purpose : it is slender, often exceeding the body in 

 length, and its pincers are small, but the grasping limb is articu- 

 lated so as to bo movable in almost any direction ; at tho proximal 

 end of tho chela3 arc ranged several groups of short bent bristles with 

 comb-liko teeth on their inner aspects. The outside of each limb of 

 the pincers carries several bundles of straight, stiff, roughened bristles, 

 so that it resembles a brush ; their inner side also carries a similar 

 series of smaller bundles, pointing towards the apex, and so arranged 

 as to interlock when the " fingers " are brought together. 



In the working of these parts in life this pair of limbs is applied 

 to all parts of tho body, and especially to tho respiratory chamber, 

 and is there moved about so as to remove foreign particles. They 

 are also used to convey to the mouth small pieces of carrion whicli 

 they have torn oft'; the animal also, according to Hcnscn's observations, 

 uses them to place grains of sand in tho auditory cavity after each 

 change of skin, as the mass of sandy otoliths is cast oft' with tho 

 skin. 



In other Shrimps, as Alphais and Palcemon, it is probably tho 

 second pair of feet which fulfils the cleansing function ; they are very 



• 'Ko8ino.s,' iv. (ISSO) p. lis. 



