BAER AND THE DEVELOPMENT OF ANIMALS 103 



of interesting- detail, and so far in advance of their age 

 that they long failed to produce their due effect. On 

 one point Malpighi unconsciously led naturalists astray 

 for a hundred years or more. On examining" a fowl's 

 egg which he supposed to be unincubated, he discovered 

 within it an early embryo. From this he concluded 

 that the embryo pre-exists in the eg-g, like a plant- 

 embryo in a seed. He mentions one circumstance 

 which makes everything- intelligible. The o^gg was 

 examined in August, during a time of great heat, and 

 the Italian summer no doubt started development, like 

 the hot sand of Aden, in which Chinamen hatch their 

 eggs. Swammerdam too enforced the same belief in 

 pre-existing germs. From the fact that the butterfly 

 can be revealed by opening the skin of a full-fed cater- 

 pillar he inferred (quite contrary to the opinion which 

 he expresses elsewhere) that one animal had formed 

 inside another. This led him to say that there is no 

 such thing as generation in nature, but merely the 

 expansion of germs which lie enclosed one within 

 another. By his theory he explained how Levi could 

 pay tribute to Melchizedek before he was born, and 

 how the sin of Adam can be laid to the charge of all 

 his posterity. The belief in the pre-existence of germs 

 was first shaken by Caspar Wolff (see p. 81), who 

 examined unincubated eggs but found no germ which 

 could be detected by the histological methods then 

 employed. 



Swammerdam's Biblia Natures contains useful figures 

 of early and late tadpoles ; in particular, he describes a 

 stage in which the body is entirely composed of rounded 

 "lumps" or "granules," the cells of modern biology. 



Early in the nineteenth century Pander and Baer, 

 both of whom were pupils of Dollinger, a teacher of 



