396 GLOSSARY 



Irritability. That power or property by which an organism is able to 



respond to stimuli. 

 Littoral. Pertaining to the shore. 



Lophophore. A disk which surrounds the mouth and bears the tentacles. 

 Medusoids. Medusa-like structures. 

 Metabolism. The process by which food is built up into living tissues, 



and living material broken up into simpler products in an organism or 



cell. 

 Milt. The spermatic fluid of fishes. 

 Myrmecophilous. Living with ants, said of insects which inhabit the 



formicaries or nests of ants. 

 Natural selection "implies that the individuals which are best fitted for 



the complex and, in the course of ages, changing conditions to which 



they are exposed generally survive and procreate their kind." — Darwin. 

 Nocturnal. Feeding or becoming active in the night. 

 Omnivorous. Eating both animal and vegetable food, feeding indis- 

 criminately. 

 Ontogeny. The development of an individual organism from its in- 



cipiency in the egg to the adult state. 

 Operculum. A lid-shaped structure closing the aperture of a tube or 



shell. 

 Ovoviparous, Viviparous. Hatching the eggs within the parent body, or 



bringing forth living young. 

 Parthenogenesis. Reproduction by supposedly unfertilized eggs. 

 Pendactyl. Having five digits. 

 Pentameral. Arranged in fives. 

 Philogeny. The study of the ancestry of organisms, or the history of 



the race. 

 Placenta. The vascular membrane which connects the embryo with the 



mother and supplies it with nutriment. 

 Poikilothermal. Having a body temperature varying with that of the 



environment. 

 Polymorphism. The condition of having many forms. 

 Precocial. Able to run about when hatched. 

 Proximal. Near the place of attachment to the body. 

 Pseudopodium. Any protoplasmic protrusion from a unicellular organ- 

 ism. 

 Recognition Mark. Coloration of special parts by which the members of 



one species may recognize their own kind, particularly beneficial in the 



recognition of parents by the young. 

 Reversion. A return toward a recent ancestral type or character. 

 Rheotropism. The directive influence upon growth exerted by currents 



of water or air. 



