GLOSSAKY. 271 



Diapophysis. The upper articular transverse costal process of 



certain vertebrae. 



Diastema. An interval in the line of teeth. 

 Digitigrade. When an animal walks on its toes. 

 Dimorphous. A species having two forms not depending on 



sex. 



Dioecious. The sexes in separate individuals. 

 Diphycercal. The tail in fishes being equal above and below, 



with the vertebral axis in the centre. 

 Diphyodont. When the earlier teeth are replaced by a second 



set. 

 Diphyzooid. A reproductive group of organs detached from the 



coenosarc of certain Calycophoridae. 

 Diploe. The cancellous layer between the two plates of a flat 



bone. 

 Diverticulum. A blind tube springing from the side of another 



tube. 

 Dolichocephaloiis. When the length of the head is more than its 



breadth. 

 Dorsigrade. When a mammal walks on the back of its toes, as in 



certain armadillos. 



Dualistic theory holds that creation was definite and purposive. 

 Duodenum. The first portion of the small intestine. 

 Dysteleology. The study relating to the " purposelessness " of 



structure or of organs. 



Ecderon. The " external plane of growth " of the ectoderm of the 

 Actinozoa. 



Ecdysis. Shedding the skin or moulting. 



Echinopadium. Prof. Huxley's name for the "worm larva" of 

 the Echinoderrnata. 



Ecthor&iim. A thread-like body continued and capable of being 

 discharged from the cnidaa of the Actinozoa. 



Ectocyst. The outer layer of the ccenoecium of the Polyzoa. 



Ectoderm (epiblast of the embryo). A multicellular membrane, 

 " the result of the segmentation of the vitellus in a true ovum " 

 (Allmaii). The external tegumentary layer of the Metazoa. 



Ectopterygoid. One of the lateral palatine bones in certain rep- 

 tiles. It is peculiarly developed in the Crocodilia. 



Ectosarc. The outer layer of sarcode in the Protozoa. 



