— II — 



This group is divided into two main sections, foreshadowing 

 a similar division in all the more specialized animal types. 



In one of these, including the rotifers, the Galyssozoa and 

 the polyzoans, the Stejitor-VikQ method of feeding by means of 

 a ciliated food-collecting mechanism, a trochal disc or a lopho- 

 phore, reappears. In the rotifers this is not accompanied by a 

 marked bodily distortion except for a prevalent asymmetry ; 

 comparable conditions, a ciliated feeding apparatus and an 

 undistorted body, subsequently occur in the sipunculids and 

 certain annelids and, also combined with asymmetry, in the 

 Gephalochorda. In the Galyssozoa and Polyzoa the animal 

 attaches by the anterior end and the mouth migrates posteriorly 

 to a position near the anus ; this curious distortion, combined 

 with a ring or group of ciliated tentacles about the mouth, is 

 repeated in Phoronis, the brachiopods, the crinoids (but not 

 the other echinoderms), Balanoglossus and Cephalodisciis^ and 

 paralleled in the tunicates. 



In the other section a ciliated or tentacular food collecting 

 mechanism is never developed ; food may be taken in either 

 of two ways, by osmosis through the body wall, as in the 

 cestodes and Acanthocephala, a method later reappearing in 

 certain parasitic molluscs and barnacles, or it may be swallowed 

 through the mouth as in most animals. 



In the acœlomate animals there are many unusual features 

 which are highly anomalous when regarded as animal structures 

 but which if met with in plant types would appear quite 

 normal. It seems logical to regard these as resulting from the 

 development of structural tendencies inherent in the organic 

 world as a whole, though ordinarily confined to the plants. As 

 a concrete illustration may be taken the occurence of chlo- 

 rophyll. The parenchyma of the species of the turbellarian 

 genus Voriex includes green vesicles containing chlorophyll 

 and starch, while some of the species of the turbellarian genus 

 Convoluta are said to be able to live on inorganic substances 

 like a green plant by means of the green cells in their tissues. 



It has been suggested that the green elements in Vortex 

 and Convohita are symbiotic alg^. If this were so these types 

 would be comparable to the lichens, which are symbiotic 

 colonies composed of Ascomycetes (more rarely Basidiomycetes) 

 living in indissoluble connection with Schizophyce^ or Ghlo- 



(400^ 



