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rophyce«. But although the occurence of symbiotic algœ has 

 been assumed in many animal types no one has ever been able 

 actually to demonstrate their existence. On the other hand 

 chlorophyll is rather widely distributed in the animal kingdom, 

 occurring in certain infusorians, sponges and cœlenterates, 

 and sporadically even as far as the insects, though confined to 

 fresh water or terrestrial types. Bearing in mind that chlo- 

 rophyll is by no means universally present in plants, being 

 entirely absent from large groups and even from a great nuniber 

 of flowering plants, we would seem justified in considering 

 chlorophyll as a potential constituent of the bodies both of 

 plants and of animals in much the same way that the carni- 

 vorous habit (developed in many bacteria, many fungi, and to 

 a greater or lesser extent even in such flowering plants as the 

 Droseraceae, Sarraceniaceœ, Nepenthacese, Cephalotaceae, Len- 

 tibulariace^E and Scrophulariaceœ) and the power of rapid 

 movement (as seen in the traps of Dionœa and Aldrovanda^ 

 the lateral leaflets of Meibomia gyrans, the lips of certain 

 orchids, the stamens of Beriberis, the leaflets and leaves of 

 Mimosa^ etc.) are potential in plants as well as in animals. 



The excretory system of the cestodes, trematodes and 

 turbellarians is most extraordinarily developed, recalling in 

 certain ways the tracheae of insects ; in its structure and 

 development, especially of its finer branches, it resembles 

 comparable organs in plants more closely than it does any other 

 organ normal to animals. In the cestodes it appears entirely 

 to replace the alimentary, circulatory and respiratory systems, 

 or rather to perform the work done by these systems in the 

 higher types, by extracting and expelling water (in addition to 

 waste products) from all the tissues of the body in this way 

 maintaining the protoplasmic density necessary to insure the 

 constant flow of nutrient liquids through the body wall and to 

 bring about the necessary interchange of substances, just as in 

 the plants the requisite protoplasmic density is maintained 

 through the exhalation of water vapor from the leaves, or better, 

 through the exudation of water from the water stomata. Intra- 

 cellular deposits recalling the raphides in the plant cells occur 

 in the mesoderm of cestodes and rotifers, and in the ectoderm 

 of turbellarians. They are also found in sponges. Spiral 

 structures, characteristic of plants but anomalous in animals, 



