Miscellaneous. 71 



parts, proceeds on the general principle that the fundamental rela- 

 tions of animals are best exhibited in the metamorphoses of species, 

 — understanding by the term metamorphosis, the series of changes 

 undergone by all animals in the progress of their development from 

 the earliest condition in the egg to the adult state ; a greater or less 

 part of which takes place in different animals within the egg state, 

 and the rest after leaving it. In 1829, Milne-Edwards brought out 

 these views, with special reference to the metamorphoses of Crus- 

 tacea ; and further showed that Crustacea have their closest resem- 

 blance to one another in their youngest age, and that the progress 

 of development from the young up, tended to imi)ress on the ani- 

 mal characters that were more and more special, and which re- 

 moved them farther from the common type of the natural group to 

 which they belonged. The same views, at the same period nearly, 

 were independently presented by the celebrated Baer, and they have 

 since been fully substantiated for the whole animal kingdom. Milne- 

 Edwards observes : — 



•' Each animal experiences a variety of modifications, some of 

 which appertain to the particular species, while others are equally 

 presented by a number, more or less large, of different animals ; and 

 the latter have a wider and wider scope, as they correspond chro- 

 nologically to a more and more early part of the series of genetic 

 phsenomena. Moreover it is easy to show that it is the general ten- 

 dency in nature to produce a correspondence between these primordial 

 resemblances of animals under development, and the different degrees 

 of zoological affinity exhibited when the species have completed their 

 development. The modifications which are manifested successively 

 in the constitution of the young, or germ, as it enlarges, determine 

 successively its existence as a member of a particular order, class, 

 and family. I am far from believing in the identity of germs. But 

 there is a resemblance, and this resemblance is close, as we approach 

 the period of their origin. Hence it is that the embryogenic history 

 of animals illustrates so fully and beautifully their natural relations." 



In carrying out these principles it becomes evident that there is a 

 natural system in animal nature, based upon a single grand prin- 

 ciple ; and further, that this system cannot be represented in a simple 

 lineal series, but must be viewed as having its affiliations or lines of 

 affinities, branching and reticulating in every direction and still sub- 

 ordinated to one plan. " There are a multitude of series which may 

 be conceived of as branching from one another at different heights, 

 or rather which are reunited at base, and separate and subdivide 

 into secondary, ternary, quaternary groups, according as they di- 

 verge and take their distinctive characters more or less near the 

 origin of their embryonic existence." 



Milne-Edwards goes on to observe, that the successive changes in 

 the organization of each animal constitute three distinct series : the 

 histogenic, or the development of the tissues ; the organogenic, or the 

 production of the organs producing physiological phaenomena ; and 

 the zoogenic, the modifications arising from the various combina- 

 tions destined to make the being a zoological unity. These divi- 

 sions are further subdivided as there are various kinds of tissues, 



