SYSTEMATIC ZOOLOGY—GILL. 465 
bryological terms—/volutio radiata, Evolutio contorta (mollusks), 
Evolutio gemina (articulates) and E'volutio bigemina (vertebrates). 
* The last were successively differentiated on account of the embryonic 
changes from the fishes to the mammals. “These Beitriige,’ Louis 
Agassiz justly affirmed, “and the papers in which Cuvier character- 
ized for the first time the four great types of the animal kingdom, 
are among the most important contributions to general zoology ever 
published.” 
One of the most notable results, so far as systematic zoology was 
involved, was the deduction forced on Kowalevsky by his investiga- 
tion of the embryology of tunicates, that those animals, long asso- 
ciated with acephalous mollusks, were really degenerate and special- 
ized protovertebrates. This view early won general acceptance. 
While embryology was very successfully used for the elucidation 
of systematic zoology its facts were often misunderstood and _per- 
verted. For instance, the cetaceans were regarded as low because 
they had a primitive fish-lke form, although it must be obvious to 
all logical zoologists of the present time that they are derived from a 
quadruped stock; snakes have been also regarded as inferior in the 
scale because no legs were developed, although it would be now con- 
ceded by every instructed herpetologist that they are descendants of 
footed or lizard-like reptiles. Ammocates was considered as higher 
than Petromyzon “inasmuch as the division of the lips indicates a 
tendency toward a formation of a distinct’ upper and lower jaw,” 
but we now know that Ammoce@tes is the larval form of Petromyzon. 
Still more pertinent examples might be adduced without number for 
the inferior systematic grades, orders, families, genera, species, ete. 
The words high and low were used when generalized and specialized 
were really meant and those words, pregnant with mischief, often 
led their users astray as well as the students to which they were 
addressed. 
PHILOSOPHICAL ZOOLOGY. 
As knowledge of the various animal groups increased and countless 
new species were piling up, yearning arose to discover principles 
underlying the enormous mass of accumulating details, and the ex- 
cogitations of various naturalists resulted in some curious specula- 
tion and expression in classificatory form. They called their out- 
pourings philosophy or philosophical zoology, and philosophers they 
were called by others. 
Some of the philosophers grouped animals according to supposed 
degrees of nervous sensibility; * some according to the relations of 
@Tamarek (1812) contended for three categories of animals: (1) Apathetic 
animals and (2) sensitive animals among the invertebrates, and (38) intelligent 
animals, equivalent to the vertebrates. 
