386 



Glossary 



PLUTEUS. Name given the charac- 

 teristic process-bearing larva of 

 sea-urchins and their near rela- 

 tives. These larvae are of con- 

 siderable general interest because 

 of the extensive use made of sea- 

 urchin eggs in experimental em- 

 bryology, the eggs being easily 

 obtained and easily kept in the 

 laboratory. 



PROTEINS. Nitrogenous substances 

 found in the bodies of plants 

 and animals. These substances 

 are usually considered to be the 

 most fundamental, from the 

 chemical standpoint, in organic 

 beings. 



PROTISTA. A group name intended 

 to include all unicellular organ- 

 isms; i.e., both protophyta, one- 

 celled plants, and protozoa, or 

 one-celled animals. 



PSEUDOPODIA. Literally false feet. 

 They are temporary protrusions 

 of the protoplasm of some pro- 

 tozoa, especially of the rhizopo- 

 dous class, typified by the amoe- 

 ba, the name having reference to 

 the locomotor office of the proc- 

 esses. But their food-taking and 

 digesting office should be noted 

 also. 



PTYALIN. The unorganized fer- 

 ment, or enzyme of saliva, chiefly 

 instrumental in the conversion of 

 starch into sugar. 



RADIOLARIA. One of the main sub- 

 divisions of the protozoa, espe- 

 cially characterized by their gen- 

 erally spherical outline, and ra- 

 diating structures, some soft and 

 extensile, others stiff and per- 

 manent. The radiolaria are al- 

 most all marine. 



REGULATION. Much used in studies 

 in the regeneration of organisms, 

 to express the power many 

 plants and animals have of un- 

 dergoing structural or func- 

 tional readjustments in order to 

 retain, or to regain, their typical 

 form; a significant adaptation of 



a general term to a technical 

 end. 



RETICULAR. Net-like, a term much 

 used in anatomy, as many por- 

 tions in both plants and animals 

 of many grades, present this 

 type of structure, though the 

 netting never has the regularity 

 of manufactured netting. 



RHIZOPODA. The great subdivision 

 of the protozoa especially char- 

 acterized by sending out pseudo- 

 podia (which see). Amoeba is 

 usually mentioned as the type of 

 this subdivision, but the larger 

 number, probably, of rhizopods 

 possess shells of one sort and an- 

 other, while amoeba is entirely 

 naked during all its active life. 



SARCODE. Literally like flesh. The 

 name originally applied to what, 

 under microscopic examination, 

 seemed to be the fundamental 

 living-substance of animals. La- 

 ter discovered to correspond to 

 what was known as protoplasm 

 in the cells of plants. 



SARCODYCTIUM. A protoplasmic 

 network of the surface of the 

 calymma of a radiolarian. 



SELF-DIFFERENTIATION, SELF-REGU- 

 LATION, &c. It is not without 

 philosophical significance that 

 the term self has forced its way 

 into technical biology, something 

 as it has into technical philoso- 

 phy. In biology the term is par- 

 ticularly common in connection 

 with developmental phenomena 

 and has reference to operations 

 which depend primarily on the 

 organism itself, and can be re- 

 ferred to "external factors" only 

 remotely and in a round-about 

 way. 



SERICTERIES. Glands by which silk 

 and silk-like substances are se- 

 creted in many insects. 



SOMA, SOMATIC. The body and 

 pertaining to the body. Much 

 used in later discussions of 

 heredity in a strongly hypothet- 



