INTERMEDIATE FORMS. 37 



If the result of the systematic sifting and arrange- 

 ment within the individual types can be comprised in 

 diagrams of trees, forms intermediate to the members 

 of the types, classes, orders, &c., follow as a matter of 

 course. For if the figure be correct, every ramification 

 of the branches must include species diverging very 

 slightly from the species standing in the lowest portions 

 of the bough from which it branches off. And thus all 

 systematizing, in fact, amounted to the insertion of the 

 right intermediate forms between each two forms devi- 

 ating from each other in a higher degree ; nay, in some 

 cases, intermediate forms were sought where none exist. 

 The older zoology always regarded the duck-mole (Or- 

 nithorhynchus) as the mammal most nearly allied to the 

 birds, though the cause of the bird-like appearance of 

 the lowest mammal known, is by no means to be sought 

 in a direct relationship, but In a remote couslnhood. 



But we must draw attention, not to these connecting 

 forms, which natural history assumes as perfectly self- 

 evident, but to those which are, as it were, inconvenient 

 to systematic description, and threaten to render Illusory 

 the groundwork so laboriously gained. There are some 

 fish-like animals, the Dipnoi, (Lepldoslrens and their 

 congeners) with the characters of Amphibians. The 

 Infusoria possess many characteristics of the so-called 

 primordial animals, but in other ways they differ from 

 them, and point to the lowest Turbellaria. A minute 

 animal inhabiting our seas in countless multitudes, i.e. 

 the Sagltta, is neither a true annelid nor a legitimate 

 mollusc. The class of the Radiata fits neither into the 

 system of the actual Annulosa, nor into that of the true 

 Articulata, yet provision must be made for it in the 



