76 HAECKEL: HIS LIFE, WORK, AND COMPANIONS 
a zoological expedition, where the master was well pleased 
with his pupil, especially with his skill in sketching the 
objects of their study ; and predicted for him a brilliant 
future. Haeckel’s Heligoland trip furnished him with 
materials for his first zoological essay. It was on the ova 
of certain fishes —the scomberesoces—and was printed in 
Mueller’s Archives for 1855. In the same volume was 
started the well-known controversy over Virchow’s conten- 
tion that each human body is a state composed of millions 
of individual cells. 
In 1855 Haeckel went to Wurtzburg, where for three 
years Virchow directed his studies. <A quarter of a century 
afterwards these two men differed as to the value of free 
discussion in matters of science ; but at Wurtzburg Haeckel 
was Virchow’s assistant, and felt nothing but admiration 
for the great pathologist and his doctrine. The burden of 
Virchow’s teaching was Monism, the unity of created 
things ; and that as the object of medical science, man is to 
be regarded as a member of the higher vertebrates subject 
to the laws of that class. Haeckel was in his twenty-first 
year, and then, as in later life, cultivated an earnest rever- 
ential spirit. His fellow students he warned against the 
evil of scepticism ; and for himself took to heart the saying 
of Faust : ‘‘ The whole sorrow of humanity oppresses me. 
Haeckel went with Kolliker in 1856 on a holiday trip 
to the Riviera. ‘Two or three cthers, and Mueller himself, 
were there at the same time; and together they caught, 
studied, and made drawings of ail sorts of living creatures. 
Haeckel carried home materials for future work ; and at 
Berlin, during the following winter, he prepared for his 
degree of Doctor, a dissertation on ‘‘ the tissues of the Cray- 
fish.’’ He tuok his degree in medicine in March, 1858 ; 
Ehrenberg, the great microscopist, presiding on the occa- 
sion. During the same year he had a friendly discussion 
with Mueller on the development of the gregarina ; and, 
before the close of the year, was stricken with grief by news 
of Mueller’s sudden death. 
