HABITS 525 



Loman describes Phoxichilidium as feeding greedily on 

 Ttibularia larynx, and especially on the gonophores. It grasps 

 them with its cla\YS, sucks them in bit by bit till the proboscis 

 is filled as far as the sieve, whereupon that part of the proboscis 

 squeezes and kneads the mass, letting only juices and fine particles 

 pass through into the alimentary canal. The lateral caeca and 

 the rectum are separated by sphincter muscles from the stomach ; 

 the former are in turn filled with food and again emptied ; the 

 contents of the alimentary canal are in constant rolling move- 

 ment, and the faeces are eliminated by the action of a pair of 

 levatores ani, in round pellets. 



The Pycnogons, or some of them, can swim by " treading 

 water," and Pcdhne is said by Cole to swim especially well ; they 

 more often progress half by swimming, half by kicking on the 

 bottom. They move promptly towards the light, unless they have 

 Hydroids to cling to, and Cole points out that when they crawl 

 with all their legs on the bottom they move forwards towards 

 the light,^ but backwards when they swim in part or whole. 

 The legs move mostly in a vertical plane, horizontal movements 

 taking place chiefly between the first and second joints. Tany- 

 stylum is uncommonly sluggish and inert ; it sinks to the 

 bottom, draws its legs over its back and remains quiet, while 

 Pcdlene, by vigorous kicks, remains suspended. 



The long legs of the Pycnogons are easily injured or lost, and 

 easily repaired or regenerated. This observation, often repeated, 

 is as old as Fabricius : " Mutilatur etiam in libertate sua, red- 

 integrandum tamen ; vidi enim in quo pedes brevissimi juxta 

 lougiores enascentes, velut in asteriis cancris aliisque redinte- 

 gratis." In such cases of redintegration of a leg, the repro- 

 ductive organ, th6 genital orifice, and the cement-gland are not 

 restored until the next moult." 



Systematic Position. — To bring this little group into closer 

 accord with one or other of the greater groups of Arthropods is a 

 problem seemingly simple but really full of difficulty. 



The larval Pycnogon, with its three pairs of appendages, 

 resembles the Crustacean Nauplius in no single feature save 



1 Loeb (Arch. Entw. Mech. v. 2, 189", p. 250) also says that the Pycnogons are 

 positively heliotro])ic. 



2 See also P. Gaubert, "Autotomie chez les Pycnogonides," Bull. Soc. Zool. Fr. 

 xTii., 1892, p. 224. 



