112 ACALETIIS IN GENERAL. Part I. 



naked-eyod Medusa^, the Hydroid.s proper, the Siphonophora?, the Milleporida^ with 

 all the Tal)ulata of Milne-Edwards, and perhaps the Rugosa also, if their trne 

 affinity is actually indicated Ijy the peculiarities of their solid parts and their 

 resemblance to those of the Tahulata. 



When considering Individuality and Specific Differences as manifested in the 

 class of Acalephs, I have taken an opportunity of showing, upon general grounds, 

 how futile the arguments are upon which the theory of transmutation of species 

 is founded. Having now shown that that class is circumscribed within definite 

 limits, I may be permitted to add here a few more objections to that theory, 

 based chiefiy upon special grounds, connected with the characteristics of classes. 

 If there is any thing striking in the features which distinguish classes, it is the 

 definiteness of their structural jteculiarities ; and this definitencss goes on increasing, 

 with new and additional qualifications, as we Y>iii^>i from the class characters to those 

 which mark the orders, the families, the genera, and the species. Granting, for 

 the sake of argument, that organized beings, living at a later period, may have 

 originated by a gradual change of those of earlier periods, one of the most 

 characteristic features of all organized iK'ings remains totally unexplained l»y the 

 various theories brought forward to explain that change, — the definiteness of their 

 respective groups, be these ever so comprehensive or ever so limited, combined 

 with the greatest inequality in their numeric relations. There exist a few thousand 

 Mammalia and Reptiles, and at least three times their number of Birds and Fishes. 

 There may be about twenty thousand Mollusks ; but there are over ouv hundred 

 thousand Insects, and only a few thousand Radiates. And yet the limits of the class 

 of Insects are as well defined as those of any other class, with the sole exception 

 of the class of Birds, which is imquestionably the most definite in its natural 

 l)Ouudaries. Now, the supporters of the transmutation theory may sliajjc their 

 views in whatever way they please, to suit the reqidrements of the theory, instead 

 of building the theory uj^on the facts of nature, and they can never make it appear 

 that the definiteness of the characters of the class of Birds is the result of a 

 common descent of all Birds ; for the first Bird must have Ijeen brother or cousin 

 to some other animal that was not a Bird, since there are other animals Ijcsides 

 Birds in the world, to no one of which does any Bird l^ear so close a relation as it 

 bears to its own class. The same argument applies to every other class. And as 

 to the facts, they are fatal to such an assumption ; for Cieology teaches us that 

 among the oldest inhabitants of our globe known, tliere are representatives of 

 nine distinct classes of animals, which by no possibility can be descendants of 

 one another, since they are contemporaries. 



The .same line of argument and the same class of facts forljid the assumption 

 that either the representatives of one and the same order, or those of one and 



