PROTOPLASMIC FUNCTION 51 



which an observation of the ameba has given us, the characteristics of 

 this animal by which it is the most typical of cells, the type of protoplasm. 

 In the first place, the protoplasm of the ameba has a certain consistence, 

 fluid yet capable of form. It has structure and organs, nucleus, cyto- 

 plasm, nucleolus, a contractile vacuole, one or more permanent vacuoles, 

 and chromatin masses in the nucleus; it is, then, a morphological thing 

 and concept. The ameba moves spontaneously and in a peculiar way 

 namely, by flowing slowly or streaming back and forth into pseudopods 

 and out again, rolling, pouring, streaming slowly over the ground. Heat, 

 up to a certain temperature, makes protoplasm more active, while 

 cold makes it less so; light affects it in this animal, and electricity influ- 

 ences it peculiarly. The protoplasm of the ameba requires oxygen, food, 

 and water in order to live; it absorbs the oxygen, digests and assimilates 

 the food, and moves only by its inherent water. Finally, a drop of proto- 

 plasm in this animal form reproduces by dividing itself into two sub- 

 stantially equal parts, which thereupon are immediately capable of all 

 the ameba's functions. 



EXPLANATION OF PLATE II. 



Plans of the nervous systems and brains of animals of widely varying complexity. Nervous 

 systems of 177, scallop (Pecten); 178, starfish (Asterias); 179, mollusc (Unio); 180, sea-mussel 

 (Mytilus); 181, a mollusc (Carinaria); 182, a mollusc (Bullea); 183, argonaut (Nautilus); 184, 

 cuttle-fish (Sepia); 185, a parasitic worm (Strongylus) ; 186, earthworm (Lumbricus); 187, a 

 rotifer (Hydatina); 188, barnacle (Lepas); 189, a marine worm (Aphroditea) ; 190, a myriapod 

 insect (Scolopendra); 191, larva of a moth-insect (Sphinx ligustri): A, cephalic ganglia; 192, 

 same at time of the first change: A, portion of thoracic cord, showing respiratory nerves; B, 

 view of ganglion from above; C, from the side; 193, nervous system of the pupa of Sphinx; 194, 

 of the imago of the same insect; 195, of the cockchaffer (Melolontha) ; 196, enteric system of 

 the locust (Gryllus migratorius) ; 197, nervous system of the sand-hopper (Talitrus); 198, crab 

 (Maia); 199, spider. In the following figures a points to the olfactory ganglia; &, to cerebral 

 hemispheres or ganglia; c, to optic lobes or ganglia; d, to the cerebellum, and e, to the spinal 

 cord: 200, brain of gurnard (fish, Trigla); 201, conger eel (Murena); 202, ray-fish (Raia); 203, 

 gray lizard; 204, frog (Rana); 205, green turtle (Testudo mydas); 206-209, development of ner- 

 vous system of the chick; 210, brain of cassowary; 211, lion; 212, origins of spinal nerves; 213, 

 nervous system of human embryo at seven weeks; 214, brain of human embryo at nine weeks; 

 215, twelve weeks; 216, fifteen weeks; 217, twenty-seven weeks; 218, 219, brain and cord of frog- 

 tadpole. (Carpenter, from many sources.) 



