GLOSSARY 243 



, -LIPASE. An enzyme which converts fats into glycerine and fatty acids. 



LIPOLYTIC. Capable of disintegrating fats. 

 MACROCYTASE. Digestive ferment of the macrophage. 



MACRONUCLEUS. The larger nucleus of a protozoan cell in which dimorphic 



nuclei are present. 

 'MATURATION. The series of processes in the formation of germ cells by 



which the number of chromosomes is reduced to one-half. 

 MEDUSA. A free-swimming, gonad-bearing sexual generation of coelen- 



terates. 



MELANIN. A toxic pigment formed by malaria organisms. 

 MERISTEM. Unformed and growing cell tissue found at the ends of young 



stems, leaves and roots. 

 MEROBLASTIC. Applied to eggs in which the division or cleavage planes do 



not cut through the yolk mass; superficial cleavage. 

 MEROZOITE. An asexually reproduced germ-cell. 

 MESODERM. The middle germ layer of an animal embryo in the three-layer 



stage. 



(^^METABOLISM. The aggregate of chemical changes in living organisms 

 involving the building up of protoplasm (anabolism), and the break- 

 ing down of protoplasm (katabolism). 

 METAGENESIS. See alternation of generations. 



/METAMERISM. Segmentation of the body along the main axis, resulting in 

 a series of more or less similar parts which are serially homologous. 

 MICROCYTASE. A digestive ferment produced by microphages. 

 . MICRONUCLEUS. The smaller nucleus of an infusorian in which dimorphic 



nuclei are present. 

 MICROSOMES. The minute granules embedded in the ground substance of 



protoplasm. 



MIMICRY. The simulation of something else in form or color, usually 

 having protective value to an organism. 



The processes^ involved in nuclear division, including formation 



^ and division of t.hft chromosomes. Same as karyokinesis. 

 , ^MORPHOLOGY. The science which deals with form. 

 MUTATION. The process of originating a new species or a new specific 



character at a single step; discontinuous variation. 



NEMATOBLAST. A nettle thread-forming cell of Hydra and allied forms. 

 NEMATODE. A round- or thread-worm. 

 NEPHRIDIUM. The excretory organ of invertebrate animals. 

 NEPHROBLAST. Initial cell of a chain of cells in development destined to 



form an excretory organ or part thereof. 

 NEPHROSTOME. Mouth or internal opening of a nephridium. 

 NEUROBLAST. Initial cell in a chain of cells in development destined to form 



the nervous system or part thereof. 



^.^NEURON. Morphological and physiological unit of the nervous system con- 

 sisting of a nerve cell, its nucleus, axon, and dendrites. 



XJ\ UCLEUS. A differentiated portion of the cell protoplasm consisting of mem- 

 brane, chromatin, linin, nucleoli and ground substance. 



