378 GLOSSARY 



Epiphytic (Gr. eVt^uw, to grow upon), used of plants growing non-para- 

 sitically upon others, as ferns, Bromeliads, etc., upon the branches of trees. 



Epithelium (Gr. tiri, upon; 6r)\(a>, to flourish), a cellular membrane 

 covering any internal or external surface. 



Evagination (Lat. ex, out of; vagina, sheath), the outgrowth or outpushing 

 of a hollow organ from within. 



Exoskdelon (Gr. ?&>, outside of), the external skeleton. 



Exuviae, (Lat. =the slough or cast skin), the cast skin of the larva at 

 metamorphosis. The word does not exist in the singular. 



Follicle (Lat. =a little bag), a small pit or bag-like hollow; in particular, 

 the hollow cellular investment of the developing ovum. 



Foramen (Lat. =a hole), a passage through any portion of the skeleton. 



Fossa (Lat. =a ditch), an external depression or hollow. 



Ganglion (Gr. ydyy\iov, a tumour), a definite swelling in the course of 

 a nerve-cord, caused by an aggregation of nerve-cells. 



Germinal Layers. In the early development of the embryo the blastoderm 

 becomes marked out into three layers of cells, of which the outermost 

 is called the ectoderm, the middle one the mesoderm, and the innermost the 

 endoderm. The term lower layer is used for the last two together, when 

 they are not clearly differentiated from one another. 



Ginglymus (Gr. yiyy\vfj.6s), a ball-and-socket joint. 



Gonads (Gr. y6vos, begetting), the organs which produce the reproductive 

 cells (sperms or ova). 



Gonapophyses (Gr. yovos, and dir6<f)v<Tis, outgrowth), appendages sur- 

 rounding the genital pore. 



Haemocoele (Gr. aipa, blood; <coiAos, hollow), a body-cavity formed by 

 secondary enlargement of the blood-spaces. 



Hamule (Lat. hamulus, a little hook), a small hook-like process. 



Histology (Gr. la-ros, a weaver's web), the science of the minute structure 

 of organisms. 



Homology (Gr. o/noAo-yew, to be in accordance with), a correspondence in 

 type of structure between parts or organs of different organisms, due to 

 evolutionary differentiation from the same or a corresponding part or organ 

 of some remote ancestor. In segmented animals, an organ of one segment 

 is serially homologous with another of another segment if the two are derived 

 from corresponding parts (e.g. thoracic legs and lateral abdominal gills). 



Hyaline (Gr. va\ivos, glassy), colourless and transparent, like glass. 



Hypertrophy (Gr. virep, over; rpo^, nourishment), excessive development 

 or overgrowth of a part. 



Hypodermis (Gr. VTTO, under-; 8epp.a, skin), in Insecta, the layer of cells 

 which lies just under the cuticle and gives rise to it. These cells are of 

 ectodermal origin. (Not to be confused with hypoblast, an alternative term 

 for endoderm.) 



Imago (Lat. =a likeness), the perfect insect. 



Instar (Lat. =an image), the stage between two successive ecdyses. 



