2 AN INTRODUCTION"- TO ZOOLOGY 



investigation of either one, it is necessary to take into consideration 

 the other, and so they are, or should be, to a considerable extent 

 complementary. 



These two main divisions are sub-divided, as has been indicated. 

 In Morphology we may consider the general external form, number 

 of parts, their relation, size, etc., and this is distinguished as gross 

 Morphology. We may also examine the actual parts, both internal 

 and external, of an animal, their general structure, relation to one 

 another, and to the body as a whole. This we term Anatomy, and 

 as a rule it necessitates the use of scalpels, scissors, etc., to dissect 

 the various structures. When this is done we may pass on to 

 consider in detail the manner in which the various parts are built 

 up, a branch of enquiry termed Histology, and requiring for its 

 pursuit a microscope, microtome, etc. This reveals the fact that 

 the whole of an animal's body is composed of, or has been derived 

 from, a series of tiny vital units termed cells, and the further more 

 intensive study of these minute particles is termed Cytology. Again , 

 all animals commence life as a small portion of living matter known 

 as an egg, a fact that is common knowledge in the case of birds, 

 butterflies, flies, etc., and we are confronted with the problem as 

 to how this comparatively simple body becomes a complex adult 

 animal. This is a branch of enquiry known as Embryology, the 

 study of development. 



Underlying all sciences are certain fundamental beliefs, and the 

 two most important of these, in the case of Zoology, are the Uni- 

 formity of Nature and Evolution. The first of these implies that the 

 various forces that we can see operating in Nature to-day have been 

 in action in times past, and will go on in the future, although it 

 may be that individual forces have varied somewhat in intensity or 

 point of application at different times, and may do so again. By 

 Evolution we mean that the various living forms that we know to-day 

 are directly derived from those that have gone before, and that in 

 turn they will give rise to those that are to come. Their diversity 

 is due to the continuous interplay of the forces included in the 

 first, acting upon and modifying successive generations of living 

 beings. It should be borne in mind, however, that these beliefs 

 do not imply an act of faith, but are simply generalised statements 

 of observations that have not been contradicted by experience. 

 As an outcome of the last, it follows that the various animals are 

 related to one another in different degrees. The last branch of 

 Morphology concerns itself with expressing these relationships as 

 accurately as our knowledge allows, by classifying and arranging 

 animals in groups and systems of groups, and when this is done 

 they are given names indicating, to a certain extent, their positions 



