4 Introduction to Animal Morphology. 



Protoplasmic motion is sometimes attended with» the 

 evolution of gas.* In an atmosphere of Hydrogen and in an 

 oxygenated solution of Haemoglobin, cilia move until the free 

 oxygen is gone {Kiihne), but under some conditions vibra- 

 tions continue for a time without oxygen and without food, as 

 if the mass had in itself a store of energy. 



The first stage of decomposition in protoplasm is 

 indicated by the formation of granules, and the disen- 

 gagement of fluid or gas making little clear spaces 

 (vacuoles). On account of the constantly occurring 

 partial contractions, homogeneous protoplasm masses 

 are rarely of large size, except where feebly acted on 

 by external stimuli ; usually they split into smaller 

 particles. The contact of air, of oxygenated water, or 

 other stimuli, seems to cause the surface to undergo 

 chemical change ; it ceases to be protoplasm, and be- 

 comes a limiting membrane,t through deficiencies in 

 which protoplasmic threads may protrude (cilia ?) 



As this material is constantly decomposing, new 

 protoplasm needs to be as constantly forming, but its 

 production is often irregular, and may proceed more 

 actively in one spot than elsewhere. Such a spot is 

 usually denser, and takes a deeper carmine dye than 

 the rest of the mass, and is often sharply defined. It 

 is called the nucleus, but it is not essential to growth,^ 



* As in Arcella {Engebimnji). Protoplasm is normally neutral or 

 slightly, alkaline, but after exhaustion of motion it is faintly acid, and some- 

 times weak alkalies revive for a time suspended motions. Possibly the 

 contraction may be the result of the force evolved by oxidation. The 

 contractions in a mass of protoplasm are always partial ; one side of a cilium, 

 or one part of a mass contracts, and drags the rest after it. The evolution 

 of light in animals is sometimes attended with the decomposition of proto- 

 plasm into urate of ammonia. t Often porous. 



t Many cells have no nuclei, as all Monera, Hydrodictyon (Alga), the 

 segmentation spheres of ova, &c. 



