206 



THE MICROSCOPE AND ITS REVELATIONS. 



Fia. 410. 



sort of tubercle. From the thorax proceed four pairs of legs, each com- 

 posed of several joints, and terminated by a hooked claw; and by these 

 members the animal drags itself slowly along, instead of walking actively 

 upon them like a crab. The mouth leads to a very narrow O3sophagus 

 (a), which passes back to the central stomach (#) situated in the midst 

 of the thorax, from the hinder end of which a narrow intestine (c) 

 passes-off, to terminate at the posterior extremity of the body. From 

 the central stomach five pairs of caecal prolongations radiate; one pair (d) 

 entering the feet-jaws, the other four (e, e) penetrating the legs, and 

 passing along them as far as the last joint but one; and those extensions 

 are covered with a layer of brownish-yellow granules, which are prob- 

 ably to be regarded as a dif- 

 fused and rudimentary con- 

 dition of the liver. The 

 stomach and its caecal pro- 

 longations are continually 

 executing peristaltic move- 

 ments of a very curious 

 kind; for they contract and 

 dilate with an irregular al- 

 ternation, so that a flux 

 and reflux of their contents 

 is constantly taking place 

 between the central portion 

 and its radiating extensions, 

 and between one of these 

 extensions and another. 

 The perivisceral space be- 

 tween the widely-extended 

 stomach and the walls of 

 the body and limbs is oc- 

 cupied by a transparent 

 liquid, in which are seen 

 floating a number of minute 

 transparent corpuscles of 

 irregular size; and this fluid, 

 which represents the blood, 

 is kept in continual motion, 

 not only by the general 

 movements of the ani- 

 mal, but also by the actions 



of the digestive apparatus; since, whenever the caecum of any one the 

 legs undergoes dilatation, a part of the circumambient liquid will be 

 pressed-out from the cavity of that limb, either into the thorax, or into 

 some other limb whose stomach is contracting. The fluid must obtain 

 its aeration through the general surface of the body, as there are no 

 special organs of respiration. The nervous system consists of a single 

 ganglion in the head (formed by the coalescence of a pair), and of another 

 in the thorax (formed by the coalescence of four pairs), with which the 

 cephalic ganglion is connected in the usual mode, namely, by two nerv- 

 ous cords which diverge from each other to embrace the oesophagus. 

 In the study of the very curious phenomena exhibited by the digestive 

 apparatus, as well as of the various points of internal conformation 

 which have been described, the Achromatic Condenser will be found use- 



Ammothea pycnogonoides: a, narrow oesophagus; & 

 stomach; c, intestine; d, digestive caeca of the feet-jaws? 

 , , digestive caeca of the legs. 



