498 
have, nevertheless, dealt with the subject 
with sufficient fullness, I hope, to convince 
you, if you were not already convinced, that 
the fundamental problems of pathology and 
embryology are alike, not only in being 
problems of cell life, but also in being simi- 
lar and even identical problems of cell life. 
Widely as the two sciences differ, they rest 
on a common foundation. 
To complete our subject it would be 
necessary to Summarize our present knowl- 
edge as to the causes of cell differentiation. 
Physiological morphology is a new science; 
we have barely crossed its threshhold, and 
are not yet at home in it. To the phy- 
sician this new science promises to far 
surpass in practical importance even the 
bacteriology of our time, since it is not pre- 
sumptuous to hope that when we under- 
stand the physiological factors, thermal, 
chemical stimulant, mechanical and other, 
which bring about structure, which cause 
cytomorphosis, we can acquire control 
over cellular differentiation, and ultimately 
be able to prevent some of the most for- 
midable diseases, over which we now 
have little or no power. The diseases 
which we may attack in the future in this 
way are diseases which may be designated 
as morphogenetic, because they are due to 
errors of morphological differentiation. At 
this vast topic it is impossible now to more 
than hint. 
Here we may stop, not because all the 
great host of relations between embryology 
and pathology have been marshaled before 
us, but because enough of these relations 
have passed us in review to present a con- 
elusive body of arguments. As we follow 
their march, we find ourselves led to the 
attack upon the problem of the causes of 
the specialization of cells, of histogenesis. 
To conquer this problem our only hope lies 
in the junction of all our forces. 
Before closing, a personal word: first, of 
sincere thanks for the honor you have con- 
SCIENCE. 
[N. 8. Vou. XIII. No. 326. 
ferred upon me both by your invitation and 
by your attention, and then a word to ex- 
press the great diffidence with which I have 
undertaken to deal with pathological phe- 
nomena. A man of science ranks accord- 
ing to the number of details which he has 
mastered, and his ability to drill them into 
coherent battalions. By no such system of 
ranking can I hope to be included among 
pathologists. I offer, therefore, only the 
thoughts of an outsider, derived from the 
long pursuit of a cognate science. Such 
external suggestions, being independent to 
some degree of pathological tradition, may 
contribute to vivify the conception of the 
unity of the biological phenomena and, 
therefore, of all forms of biological investi- 
gation. It will be a service rendered if my 
words recall the great truth that biology 
is not a congery of sciences, but a single 
science, which we artificially divide and 
subdivide until the parts are commensurate 
with our mental capacity. In the truest 
sense we are fellow-workers. Let us, there- 
fore, work together. 
CHARLES SEDGWICK Minor. 
THE DETERMINATION OF THE TYPE IN 
COMPOSITE GENERA OF ANIMALS 
AND PLANTS. 
To the older naturalists a genus was a 
subdivision of an order containing a num- 
ber of species, each standing in like rela- 
tions to the. genus. The genus was a 
pigeon-hole into which species of similar 
characters were thrust. 
In the modern conception a genus is a 
group of related species, associated about a 
single one which is the type of the genus. 
In theory this type should be the central 
species or the most primitive one. In the 
exigencies of nomenclature, it is the one 
which was in point of fact first associated 
with the generic name. Modern writers 
recognize this grouping of species about the 
generic type, and to each new genus of 
