through my whole life the perfectly clear conviction that when I had
mastered a whole subject in its intimate relations I could go back upon,
and then understand, details which at the time of hearing had been
unintelligible to me.

In botany I had a clear-sighted, kind-hearted teacher (Batsch). His
natural system of botany[20] gave me great satisfaction, although I had
always a painful perception of how much still remained for him to
classify. However, my view of Nature as one whole became by his means
substantially clearer, and my love for the observation of Nature in
detail became more animated. I shall always think of him with gratitude.
He was also my teacher in natural history. Two principles that he
enunciated seized upon me with special force, and seemed to me valid.
The first was the conception of the mutual relationship of all animals,
extending like a network in all directions; and the second was that the
skeleton or bony framework of fishes, birds, and men was one and the
same in plan, and that the skeleton of man should be considered as the
fundamental type which Nature strove to produce even in the lower forms
of creation.[21] I was always highly delighted with his expositions, for
they suggested ideas to me which bore fruit both in my intelligence and
in my emotional nature. Invariably, whenever I grasped the
inter-connection and unity of phenomena, I felt the longings of my
spirit and of my soul were fulfilled.

I easily understood the other courses I attended, and was able to take a
comprehensive glance over the subjects of which they treated. I had seen
building going on, and had myself assisted in building, in planting,
etc.; here, therefore, I could take notes, and write complete and
satisfactory memoranda of the lectures.

My stay in Jena had taught me much; by no means so much as it ought to
have taught me, but yet I had won for myself a standpoint, both
subjective and objective. I could already perceive unity in diversity,
the correlation of forces, the interconnection of all living things,
life in matter, and the principles of physics and biology.

One thing more I have to bring forward from this period. Up till now my
life had met with no sympathetic recognition other than the esteem which
I had enjoyed of the country physician during my apprenticeship--he who
encouraged me to study natural science, and smoothed away for me many a
difficulty. But now such sympathy was destined to offer itself