Ixvili | REPORT—1858. 
primary group of animals, the Vertebrata. The next step of importance will 
be to determine the homologous parts of the nervous system, of the muscular 
system, of the respiratory and vascular system, and of the digestive, secre- 
tory, and generative organs in the same primary group or province. I think 
it of more importance to settle the homologies of the parts of a group of 
animals constructed on the same general plan, than to speculate on such re- 
lations of parts in animals constructed on demonstratively distinct plans of 
organization. What has been effected and recommended, in regard to homo- 
logous parts in the Vertebrata, should be followed out in the Articulata and 
Mollusca. 
In regard to the constituents of the crust or outer skeleton and its append- 
ages in the Aréiculata, homological relations have been studied and deter- 
mined to a praiseworthy extent, throughout that province. 
The same study is making progress in the Mollusca ; but the grounds for 
determining special homologies are less sure in this subkingdom. The 
vegetative functions here predominate ; and just as the organs of these func- 
tions are less satisfactory subjects of homological determination than those of 
the animal functions in the Vertebrate province, so the Molluscous province 
is a less favourable field for homological demonstrations than either the 
Articulate or Vertebrate provinces, in which the animal functions predomi- 
nate over the vegetative. 
So far as homologies can be determined, within the limits in which such 
determination can be most satisfactorily carried out, the foundation will be 
securely laid for a superstructure of higher generalizations in regard to parts 
homological or answerable throughout the animal kingdom generally. 
The present state of homology in regard to the Articulata has sufficed 
to demonstrate that the segment of the crust is not a hollow expanded homo- 
logue of the segment of the endoskeleton of a vertebrate. There is as little 
homology between the parts and appendages of the segments of the Verte- 
brate and Articulate skeletons respectively. The parts called mandibles, 
maxilla, arms, legs, wings, fins, in Insects and Crustaceans, are only ¢ analo- 
gous’ to the parts so called in Vertebrates. 
To express finitely the clear deideas now possessed of their essential di- 
stinction, will require a distinct nomenclature. The same remark is appli- 
cable to other systems of organs. The so-called ‘lungs’ of the spider are 
analogous to, not homologous with, our ‘lungs :’ the trachez of insects are 
not homologous with the bird’s trachea and its ramifications: the gills of 
the lobster are not the homologous parts of the gills of fishes. No compara- 
tive anatomist now supposes that the heart of the lobster is homologous with 
that of a fish: or either of these organs with the heart of a snail. ‘The name 
in each group is simply expressive of similarity of function, and of connexions 
limited by and solely related to such function, as of the heart with a vein 
and an artery. A most extensive field of reform is becoming open to the 
homologist in that which is essential to the exactitude of his science—a no- 
