Calcispongige in the Animal Kingdom. 2G1 



irreconcilable representations which have been given within 

 the last few years of the embryology of many Vertcbrata and 

 Arthropoda. This chaotic condition of animal ontogeny may 

 certainly in part be excused by the difficulty of the subject 

 and the various methods of observers. But for the most part 

 it is due to the fact that most ontogenists work without any 

 method at all, — that is, if we understand by the term scientific 

 method of investigation a thoughtful and systematic compre- 

 hension, a comparative treatment and a philosophical develop- 

 ment of the problem, and not merely the empirico-technical 

 treatment of the object with anatomical instruments and 

 chemical reagents. 



No doubt the present state of embryology would be much 

 more satisfactory if most embryologists did not entirely turn 

 away their eyes from those two guiding-stars which alone are 

 able to lead to the goal in the difficult and obscure paths of 

 ontogeny, namely comparative anatomy and phylogeny. In 

 most embryological treatises we see at the first glance that 

 their authors are not well acquainted with comparative 

 anatomy (as it is treated, for example, in the classical "Grund- 

 ziige" of Gegenbaur), and that they know little more than 

 the individual animal, or the particular group of animals, 

 whose development they are studying. But, for the compre- 

 hension of the higher animals, a thorough knowledge of the 

 comparative anatomy of the lower animals is indispensable. 

 And it is equally indispensable to every good ontogenetic 

 investigation that phylogeny should be constantly taken into 

 consideration. Many false embryological theories would have 

 been quite incapable of establishing themselves if they had 

 been looked at in the light of the descendence-theory and 

 with reference to phylogeny*. Comparative anatomy, on- 



* The value of the ontogenetic theories which have been proposed 

 without reference to phylogeny appears clearly from the following fact : — 

 In one and the same vertebrate {e.g. the common fowl) one group of 

 observers still find that the middle germ-lamella originates from the 

 upper, and a second gi-oup that it originates from the lower germ-lamella ; 

 a third group find that the upper half of the middle germ-lamella (the 

 skin-lamella) originates from the dermal lamella, and its lower half (the 

 intestino-fibrous lamella) from the gastral lamella. Again, some embryo- 

 logists make the sexual organs originate from the upper, others from the 

 middle, and others from the lower lamella. Similar differences prevail 

 with regard to the origin of other organs. Now, as every observer assures 

 us that his observation is the coiTect one, and all others are erroneous, 

 the phylogenist who desires to recognize with certainty at least the most 

 important principles of phylogeny from these ontogenetic facts finds 

 himself quite helpless before them. 



As regards the origin of the mesoderm, it must be added to what has 

 already been said oii the subject (pp. 2.j7, 258) that the third view just 



