EVIDENCE FROM COLONIAL OR COMPOUND ANIMALS. 275 



an " ovum " or " egg." As the result of the development of that 

 egg, the animal body becomes the adult ; and of the plant the same 

 truth holds good. The seed or germ undergoing development, and 

 passing through stages which are, as a rule, of well-defined nature, at 

 last appears before us as the perfect plant, which, in its turn, will 

 produce blossom and fruit, and will finally lead us back once more 

 to the seed and germ. One marked and very obvious difference 

 between high animals and low animals is found to exist in the dif- 

 ferent results to which development leads. The lower animal's 

 growth ceases, and its adult condition is attained, at a stage when 

 the development of the higher being has barely begun. It takes but 

 little trouble on nature's part, so to 

 speak, to convert the matter of life of 

 a low animal or plant into a form 

 like itself. On the other hand, the 

 development of a higher animal means 

 time and trouble, to use a familiar 

 expression, and entails the elaboration 

 and building of a complex body from 

 that which is invariably in its first 

 stages uniform and simple in structure. 

 Such an animal form as a Gregarina 

 (Fig. 183, d), for instance, presents us 

 with a good example of that simplicity 

 of development and that primitiveness 

 of personality which marks the lower 

 fields of animal life. A gregarina is a 

 minute speck of protoplasm found in- 

 habiting the digestive canal of worms, 

 insects, and crustaceans, as an internal 

 parasite. Each gregarina lives what 



may be described as the simplest form of existence. Existing in 

 the digestive system of its host, it literally lies bathed amidst the 

 nutriment which that host is elaborating for the repair of its own 

 tissues. Possessing no traces of any of the organs belonging to 

 higher animal existence, the gregarina lives by the absorption of 

 the digested fluids of its host ; and save for the slow contractions 

 which are sometimes seen to pass in waves along the surface of its 

 body, no movements can be observed whereby its animality might 

 be popularly confirmed. The course of gregarina-development is by 

 no means complex. The body itself, in lieu of an egg or germ, will, 

 sooner or later, become of globular shape (). The little solid body, 

 or " nucleus," seen normally (d) in its interior, will vanish by a kind 

 of physiological necromancy, and the body-substance itself will break 

 up and divide into spindle-shaped masses (a), for which the thickened 



T 2 



FIG. 183. GREGARINA AND ITS 

 DEVELOPMENT. 



