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 cousinhood. 
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, (Lepidosirens 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, ze. 
the Sagitta, 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 
