— i3 — 



are represented by the spiral reinforcement of various organs 

 (pharynx, vagina, etc.) and sometimes of the whole body seen 

 in certain nematodes, recalling the trachea of insects, and in 

 the nematocysts. These last occur in certain infusorians, in all 

 the coelenterates, in the single genus Euchlora among the 

 ctenophores, in the ^Eolidiodea among the naked molluscs, 

 on the surface of the proboscis in the unarmed nemerteans, and 

 in the ectoderm of the turbellarians belonging to the genera 

 Microstoma, Anonymus and St/lochoplana. Intracellular canals, 

 characteristic of plants, occur in certain types, and in the 

 nematodes the alimentary tract may be, like tracheal tubes, 

 secreted by a single cord or spiral coil of cells, while in the 

 male rotifers it is sometimes replaced by a simple string of 

 cells. Excepting for the more or less Stentor-WkQ rotifers, 

 Calyssozoa and polyzoans the acœlomate animals are all either 

 much flattened, or elongate and cylindrical, often filiform 

 possessing therefore the body form characteristic of plants 

 in contrast to that normal for animals. They develop mostly 

 from a solid more or less phanerogam-like embryo either 

 gradually and directly into the adult or through an asexual 

 stage very different from the adult which undergoes vegetative 

 reduplication by budding and fission ; in both of these features 

 the development resembles that of plants more than of the 

 higher animals, excepting only for one or two highly anomalous 

 crustaceans. 



Together with the features just mentioned there are others, 

 such as distinct traced of radial and bilateral symmetry, 

 which recall the coelenterates and ctenophores, and still others, 

 especially in connection with the parenchyma, which recall 

 the sponges. 



The characters of the acœlomate animals may be analyzed, 

 as follows : 



Features duplicated in the plants, but not in the 



simpler multicellular animals (i i) 44 % 



Features found in higher animals (7) 28^/0 



Features characteristic of the Infusoria (4) 16 % 



Features characteristic of the sponges (i) 4 °/o 



Features characteristic of the coelenterates (i.)... 4 Vo 

 Features characteristic of the ctenophores (i).. . . 4^/0 



(400) 



