PROF. HAECKEL has recently published his reply to the address on “The Liberty of Science in the Modern State,” delivered at last year's meeting of the German Association, by Prof. Virchow. If we enter into this subject at greater length than is our custom with pamphlets we do so mainly from a sense of common fairness to both parties, since we reproduced Prof. Virchow's address in extenso (NATURE, vol. xvii. pp. 72, 92, and; 111). We shall, however, confine ourselves merely to brating Prof. Haeckel's views on the subject, and leave it to our readers to judge of the value of his remarks for themselves.