266 GLOSSARY. 



Biotome (Cobbold). " A successive life-epoch in the development 



of some of the lower animals," e. g. Entozoa. 

 Blastema. A mass of formative matter. 

 Blastocheme. " A medusiform planoblast which gives origin to 



the genei'ative elements, not directly, but through the medium 



of special sexual buds which are developed from it " (Allmari). 

 Blastocotle. The cavity of the morula. 

 Blastoderm. The outer membrane of the embryo. 

 Blastomeres. Division-masses or germ-masses. The divisions of 



the germ ; these become cells and give rise to tissues. 

 Blastopore (Ray Lankester). The orifice of the invagination in 



certain invertebrates, either becoming a mouth or eventually 



closing up. 



Blastosphere. Blastomeres arranged in a hollow sphere. 

 Blastostyle or gonoblastidium. " A columniform zooid destined 



to give origin to generative buds " (Allmati). 

 Brachycephalous. When the breadth of the head is more than 



its length. 



Branchiae = gills. The organs in which the venous blood is oxy- 

 genized. 

 Bronchi. The branches of the windpipe conveying the air to the 



lungs. 



Bulbus arieriosus. The dilated base of the arch of the aorta. 

 Byssus. The filamentous substance secreted by the mouth of 



certain bivalve Mollusca. 



Cacum. A blind pouch opening into the duodenum. 



Cainozoic. The Tertiary period. 



Calamistrum. Two rows of movable spines on the metatarsal 

 joints of each posterior leg of certain spiders form an appara- 

 tus called a calamistrum. 



Calcaneum. The heel-bone or os calcis. 



Calicle. The cup-like excavation terminating the theca of a 

 corallite. 



Calycle or hydrotheca. The receptacle in which the polypites 

 are lodged in the Calyptoblastea. 



Canthus. The angles or corners of the eyes. In certain insects 

 it is a process of the clypeus partially or completely dividing 

 the eye. 



Carapace. The dorsal plate of the Crustacea and Chelonia. 



