i 4 COMPARATIVE ANATOMY 



dissection and microscopical study. The student will find 

 full instruction for the detailed examination of the common 

 forms of animal life dealt with in this book in the excellent 

 practical manuals, * published by the late Professor A. Milnes 

 Marshall. As this work is intended to supplement, not to 

 supersede, practical work carried on by aid of these books, 

 attention will be given rather to the lessons which may be 

 learned and the conclusions which may be drawn from 

 anatomical and embryological facts than to the detailed ex- 

 position of the facts themselves. The frog, however, being 

 taken as a type of animal structure, will be described in 

 detail. 



We must bear in mind, before we embark on our practical 

 studies, that the object of our practical and literary studies in 

 Zoology is to furnish the mind with clear ideas on animal 

 structure and organisation, and to this end our ideas must be 

 arranged in an orderly and methodical fashion. We must 

 accustom ourselves, from the outset, to think of the organs 

 and tissues of the animal body in a definite order, so that 

 they may readily be called up to our minds without haziness 

 or omission. The order in which we shall deal with the 

 anatomical facts exposed by dissection will not necessarily be 

 the same as that in which they are discovered in the course of 

 practical work. In any animal of complex structure the 

 various organs are so interwoven with one another, and in 

 such different manners in different types of organisation, that 

 it is generally necessary to take into account several systems 

 of organs in the course of any piece of dissection. Moreover, 

 it will frequently be necessary to cut away and destroy one 

 organ in order that another may be exposed. Hence the 

 lessons learned from dissection are apt to confuse us at first 

 unless we deal with them in a methodical manner, keeping 

 our attention fixed upon one set of organs at a time, and 

 eventually constructing a plan of that system from the results 

 obtained by our various dissections. But, whilst we deal with 

 organs and systems of organs in a methodical manner, we 



* THE FROG : an Introduction to Anatomy, Histology and Embryology. 

 By A. Milnes Marshall. Sixth Edition. Edited by G. Herbert Fowler. 

 London : D. Nutt. 1897. 



A JUNIOR COURSE OF PRACTICAL ZOOLOGY. By A. Milnes Marshall 

 and C. Herbert Hurst. Fifth Edition. London : Smith, Elder & Co. 



