474 GENERAL ZOOLOGY 



expended in lifting it. An organic compound possesses potential 

 energy in a chemical form in proportion to the energy expended in 

 establishing a certain spatial relation between atoms in the molecule. 

 Preformation. In its original form, the idea that development consisted 

 in the unfolding of adult structures already preformed in the germ; 

 which, of course, can no longer be accepted. In a modified sense the 

 term can be applied to the organized ground substance of the egg and 

 to the orderly arrangement of genes in a chromosome. 

 Proboscis. A tubular process or prolongation of the head or oral region. 

 Protandry. A condition in monoecious animals in which the testis 



becomes functionally mature before the ovary. 

 Protein. An organic compound of large molecules made up of carbon, 

 hydrogen, oxygen, nitrogen, and sulphur with sometimes phosphorus 

 and iron which upon hydrolysis yields amino acids. A very important 

 constituent of protoplasm and one which has not yet been synthesized. 

 Protoplasm. Living matter. 



Prototheria. The lowest group of mammals, which are oviparous. 

 Protozoa. Unicellular animals. 



Proximal. Next or nearest, as to a point of attachment. 

 PsETjDOPODiUM. A temporary fingerlike extension of the cytoplasm of 



Amoeba and related forms. 

 Pulmonary. Pertaining to the lung. 

 Pupa. The quiescent stage following the larval period in an insect, during 



which the adult organs are developed. 

 Pure line. All the offspring of a homozygous self-fertilized parent. A 



group of individuals having an identical germinal constitution. 

 Putrefaction. The decomposition of proteins as brought about by 



enzymes or bacteria. 

 Radial symmetry. Symmetry that is referable to a circle. Two or more 

 planes passing through a common axis will in each case produce halves 

 that are mirrored images of each other. 

 Receptor. A sensory-nerve ending or end organ. 

 Rectum. The terminal portion of the alimentary canal in vertebrates and 



in many invertebrates. 

 Reducing agent. A chemical agent which causes a loss of oxygen in a 



substance. 

 Reduction division. One of the two maturation divisions in gametogene- 

 sis during which synaptic chromosome mates separate, reducing the 

 number to one-half. 

 Refractive. Having power to turn from a direct course. Said of the effect 



of certain substances on light. 

 Respiration. The absorption of gaseous oxygen and the excretion of 



carbon dioxide by protoplasm. 

 Response. Any change in protoplasmic activity resulting from a stimulus. 

 Reticulum. A network. 



Ruminant. A herbivorous animal that chews its cud. 

 Sacral. Pertaining to the region of the vertebrate axial skeleton to which 

 the pelvic girdle is attached. 



