726 
he was at Sheen Lodge, Richmond Park. 
While in Germany he attended the meeting of 
German Naturalists and Physicians at K6n- 
igsberg, of which he has left an interesting 
account in his notes of European travel. 
In the spring and summer of 1861 he gave 
a course of lectures on histology at the Mu- 
seum of Comparative Zoology. One of his 
friends writes: 
I remember his interesting lectures before our 
small class on cellular structure in plants and 
animals. His skill with the microscope and his 
rare ability to draw aided him greatly in making 
out the minutest details of cell structure. His 
personal qualities were of a kind to endear him to 
many friends, especially to those students who 
sought and obtained from him counsel and advice 
in their studies, as I did on many occasions. 
The small class included Hyatt, Morse, 
Packard, Putnam, Scudder, Shaler and Ver- 
rill. 
Notwithstanding his constant investiga- 
tions, Professor Clark found: time to prepare 
a course of twelve lectures—the result of his 
microphysiological studies—which he deliv- 
ered at the Lowell Institute in the winter of 
1864. These were subsequently rewritten and 
published in 1865, under the title of “ Mind 
in Nature; or the Origin of Life, and the 
Mode of Development of Animals.” This 
work, based on structure and development in 
the animal kingdom, is crowded with original 
observations and testifies to years of the 
severest labor and independent thought. “ It 
is in all respects,” says Packard in 1873, “ for 
its usually sound and clear thinking, its 
breadth of view and the amount of original 
work it contains, perhaps the most remark- 
able general zoological work as yet produced 
in this country.” 
Clark adopted and strongly urged the doc- 
trine of spontaneous generation, from the 
facts afforded by the experiments of Jeffries 
Wyman, and on the question of evolution 
adopted views resembling those of Richard 
Owen. The original matter in the book is 
that relating to the structure of Bacterium 
termo and Vibrio bacillus, the theory of the 
egg and its polarity and bilaterality, and the 
SCIENCE 
[N.8. VoL. XXXV. No..906 
cellular structure of Actinophrys, with many 
other new points relating to the anatomy and 
physiology of the Protozoa and Radiates. It 
anticipated also certain points in histology, 
and the structure of the Protozoa and Sponges 
especially, which have made the succeeding 
labors of some European observers notable. 
In 1866 Professor Clark accepted the chair 
of botany, zoology and geology at the Agricul- 
tural College of Pennsylvania, where he re- 
mained three years, exchanging it in 1869 for 
similar duties at the University of Kentucky. 
Neither of these posts was agreeable to his 
taste, chiefly on account of the pressure of col- 
lege duties, which left him but little time for 
abstract investigations. It was, therefore, 
with great readiness he accepted the call to 
this college in 1872. 
Here his duties were of a more congenial 
nature, and he applied himself with renewed 
energy to teaching and soon began the for- 
mation of a museum—a working collection of 
comparative and pathological anatomy. Turn- 
ing to his first and only report—remarkable 
for its clearness, particularity and insight— 
we find that he taught human anatomy and 
physiology, comparative anatomy and zoology, 
and comparative physiology. These studies 
were to form the groundwork for a course in 
general and veterinary pathology. He lays 
stress on the importance of the objective 
method of teaching in the class-room and of 
laboratory instruction. ‘“ Having mastered,” 
he says, “the general principles of structure 
and relation throughout the length and 
breadth of the animal kingdom, the rawness 
of total ignorance is supplanted by a new 
habit of thought, and a proneness to make 
further inquiry upon meeting with any object 
in nature. Here, then, comes the time for 
laboratory practise. Supplied with scalpel 
and magnifier, the student should be required 
to work out topics upon unprepared speci- 
mens. If he has acquired the smallest grain 
of interest in the matter previously, patience 
will enter where it could not possibly have ex- 
isted before. _He learns the art of seeing and 
knowing what he looks at; he becomes by de- 
grees an observer; and in doing that, he is 
