366 ANIMAL BIOLOGY. 



Amoeboid. A term applied to cells which change their form like the 

 amoeba. 



Anabolism. See Metabolism. 



Analogous Organs. Organs which perform the same function, but are not 

 necessarily constructed on the same plan ; used in contradistinction to 

 homologous organs, when they are constructed on the same plan, but 

 have not necessarily the same function. The wing of the insect and 

 that of the bird are analogous, but not homologous ; the wing of the 

 bat and the paddle of the whale are homologous, but not analogous ; 

 the hind-limbs of the frog and the rabbit are both analogous and 

 homologous. 



Anastates. See Metabolism. 



Aponeurosis. The strong sheath of connective tissue which invests a 

 muscle. Those covering the muscles have been termed aponeuroses 

 of investment, in contradistinction to the tendinous expansions or 

 aponeuroses of insertion. 



Appendicular. Applied to that part of the vertebrate skeleton which is 

 related to the appendages, as opposed to the axial skeleton. 



Archenteron. The digestive cavity of the embryo at the gastrula stage. 

 After the formation of the mesoblast the term mesenteron is employed. 



Arterial. A term applied to blood which has been oxygenated in the lungs 

 or gills, opposed to venous when the oxygen has been used up by the 

 tissues. The pulmonary artery contains venous blood, the pulmonary 

 vein arterial blood. 



Articulation. Union at a joint. The lower jaw is articulated to the skull. 



Atrophy. The wasting away of a part or organ. 



Axial. See Appendicular. 



Biogenesis. See Abiogenesis. 



Blastoccele. Also called segmentation cavity; the cavity contained within 

 the blastosphere or hollow mass of cells (blastomeres) resulting from the 

 segmentation of the ovum. Where segmentation gives rise, as in the 

 fowl, to a cellular patch, it is termed the blastoderm. The hollow 

 mass of cells produced by segmentation in the rabbit is termed the 

 blastodermic vesicle. The blastopore is the orifice of the archenteron 

 of the gastrula, produced by the invagination of the blastosphere. 



Budding. The asexual formation of new individuals, in hydra, by the 

 formation of a pear-shaped outgrowth which develops into a new 

 hydra. The process is also called gemmation. 



Caecum. A blind pouch. 



Canaliculi. Minute tubes arising from the lacunae of bone, or from the 



repeated branching of the hepatic ducts. 

 Capillaries. The finest and most delicate blood-vessels, formed by the 



ultimate subdivision of the arteries, and giving rise to the most minute 



factors of the veins. 



