GLOSSARY 539 



Tentacula or Tentacles — Delicate fleshy organs of prehension or touch pos- 

 sessed by many of the lower animals. 



Tertiary — ^l"he latest geological epoch, immediately preceding the establish- 

 ment of the present order of things. 



Trachea — -The windpipe cr passage for the admission of air to the lungs. 



Tridactyle — Three-fingered, or composed of three movable parts attached 

 to a common base. 



Trilobites — A peculiar group of extinct Crustaceans, somewhat resembling 

 the Woodlice in external form, and, like some of them, capable of 

 rolling themselves up into a ball. Their remains are found only in 

 the Palaeozoic rocks, and most abundantly in those of Silurian age. 



Trimorphic — Presenting three distinct forms. 



UmbellifercB — An order of plants in which the flowers, which contain five 

 stamens and a pistil with two styles, are supported upon footstalks 

 which spring from the top of the flower stem and spread out like 

 the wires of an umbrella, so as to bring all the flowers in the same 

 head (.umbel) nearly to the same level. (Examples, Parsley and 

 Carrot.) 



Ungulata — Hoofed quadrupeds. 



Unicellular — Consisting of a single cell. 



Fa5CM/ar— Containing blood-vessels. 



Vermiform — Like a worm. 



Vertebrata; or Vertebrate Animals — The highest division of the animal 

 kingdom, so called from the presence in most cases of a backbone 

 composed of numerous joints or vertebra, which constitutes the cen- 

 tre of the skeleton and at the same time supports and protects the 

 central parts of the nervous system. 



Whorls — The circles or spiral lines in which the parts of plants are 



arranged upon the axis of growth. 

 Workers — See Neuters. 



Zoea-stage — The earliest stage in the development of many of the higher 

 Crustacea, so called from the name of Zo'ea, applied to these young 

 animals when they were supposed to constitute a peculiar genus. 



Zooids — In many of the lower animals (such as the Corals, Medusie, &c.) 

 reproduction takes place in two ways, namely, by means of eggs and 

 by a process of budding with or without separation from the parent 

 of the product of the latter, which is often very different from that 

 of the egg. The individuality of the species is represented by the 

 whole of the form produced between two sexual reproductions; and 

 these forms, which are apparently individual animaJs, have been 

 called sooids. 



