Phylogeny of Animals 519 



segment in front, and at times directed downward, "as if in- 

 vestigating the nature of the rocks on which it may settle," 

 at the same time often rotating it. 



When the larva fixes by its pedal end, changes occur and 

 stiuctures can be traced that can best be interpreted if we 

 keep in view a possible rotiferan ancestry. 



When the larva fixes dow^n, the skirt, at least in some cases, 

 becomes slipped forward so as to encircle the head, and gives 

 rise to the adult mantle lobes, a development that does not 

 seem to be reached by any rotifer, and then gradual degen- 

 eration of the eyes takes place. In relation to rotifers the 

 formation of the first or embryonic shells is highly suggestive. 

 In that group is included a large and varied division known 

 as the "loricata," or shelled rotifers. In these, two distinct 

 chitinous plates or shells are formed, one on the dorsal, the 

 other on the ventral, surface of the animal, and are well exem- 

 plified in Monostyla, Diplax^ and Cathypna; or instead and 

 more rarely two latero- ventral plates may be formed. In 

 various ancient and recent brachiopods similar shells occur, 

 the dorsal plate being termed the prodeltidium, the ventral 

 the deltidium. These undergo various modifications as the 

 adult shell is deposited aiound them in the form of dorsal 

 and ventral secretions. Such a feature might suggest that 

 the Brachiopoda sprang from a loricate member of the Roti- 

 fera, and this is possibly further strengthened by the fact that 

 most of the marine rotifers now living are included in the more 

 evolved loricate section. 



As the fixed and maturing larva passes into the adult, the 

 brain, or supra-oesophageal ganglionic mass, grows in from 

 the antero-dorsal epidermis as in rotifers, and similarly retains 

 connection with the epidermis. Sub -oesophageal ganglia and 

 longitudinal nerves complete the resemblance. 



But the most striking structures of adult brachiopods are 

 the two long and coiled "arms." These arise as lobular ex- 

 pansions on either side of the mouth, and alike in oiigin, posi- 

 tion, function, and relative size correspond to the huge trochal 

 discs seen in such a loricate rotifer as Brachionus, or the even 

 larger ones of Floscidaria^ Melicertay and Limnias. 



A possibly trivial feature, but one nevertheless that may 

 indicate parallelisms in evolution, is the blind ending to the 

 intestine in Asplanchna and Paraseison among rotifers, and 

 in the higher group or Testicardines of the ]5racliiopoda. 



The primitive kidneys in both are elongated tubules that 

 run forward to the oral and trochal region, and in both groups 

 these end in flame- or funnel-shaped inner endings. 



