GLOSSARY. 371 



division of labour has taken place : used in contradistinction to 

 protozoa where there is generally but one cell, or at most an aggregate 

 of similar cell units. Sometimes called histozoa. 



Morphology. That branch of the science which deals with the form and 

 structure of organs or organisms : whereas physiology deals with their 

 functions ; and histology with their minute structure. Morphological 

 structure is ascertained by anatomical investigation. 



Morula. A mulberry mass of cells not enclosing a cavity, and resulting 

 from segmentation. 



Neural (1) Neural folds, groove, and tube (often called the medullary 

 folds, tube, etc.), the first indications of the cerebro- spinal nervous 

 system ; (2) Neural arch and spine, processes of the vertebrae. 



Notochord. A rod of cells derived from the hypoblast, and underlying 

 the neural tube. It forms the primitive axial support of the body. 

 Sometimes called the chorda dorsalis. 



Nucleus. The specially differentiated 'kernel* of a cell in which all vital 

 changes seem to be initiated. Within the nucleus there may be one 

 or more nucleoli. 



Oral. The oral end of an organism is that part which bears the mouth. 

 The opposite end is called aboral. 



Origin. (1) ^Etiological questions are spoken of as questions of origin 

 (e.g. origin of species, origin of tissues). (2) The relatively fixed 

 point to which a muscle is attached is termed its origin, in contra- 

 distinction to the relatively moveable part where it has its insertion. 



Otoliths. Concretions or foreign particles in an auditory sac. 



Ovo-testis. Also called hermaphrodite gland. An organ or gonad which 

 produces both ova and spermatozoa. 



Ovum. The cell produced by the female, from which, generally after 

 fertilisation by a spermatozoon, a new organism arises. Such repro- 

 duction is called sexual : where the organism is reproduced without 

 ova (e.g. by budding or fission), the reproduction is called asexual. 

 When the ovum develops without fertilisation the term partheno- 

 genesis is used. 



Palp. A process supposed to be an organ of touch generally in relation to 

 the mouth (e.g. labial palps of mussel, mandibular palp of crayfish). 



Pancreas. A vertebrate digestive gland. The invertebrate digestive gland 

 (e.g. of crayfish) is sometimes called the hepato-pancreas. 



Papilla. A small projection (e.g. of the tongue). 



Parietal. (1) A bone of the skull which gives its name to one of the 

 segments of the brain-case. (2) Of or belonging to the parietes or 

 walls, e.g. parietal (or somatic) layer of the peritoneum, in contra- 



