200 THE HISTORY OF CREATION, 
vol. i. p. 303.) In all Vertebrate animals without exception, 
man included, these important parts of the body during 
the embryological development out of the egg, originally 
begin in the same simple form, which is retained throughout 
life by the Amphioxus. It is only at a later period that the 
brain develops by the expansion of the fore end of the spinal 
marrow, and out of the spinal rod the skull which encloses 
the brain. As these two important organs do not develop 
at all in the Amphioxus, we may justly call the class repre- 
sented by it, Skull-less animals (Acrania), in opposition to 
all the others, namely, to the animals with skulls (Craniota). 
The Skull-less animals are generally called tubular-hearted 
(Leptocardia), because a centralized heart does not as yet 
exist, and the blood is circulated in the body by the con- 
tractions of the tubular blood-vessels themselves. The 
Skulled animals, which possess a centralized, thick-walled, 
bulb-shaped heart, ought then by way of contrast to be 
called bulbular-hearted animals (Pachycardia). 
Animals with skulls and central hearts evidently developed 
gradually in the later primordial period out of those without 
skulls and with tubular hearts. Of this the ontogeny of 
skulled animals leaves no doubt. But whence are these 
same skull-less animals derived ? It is only very lately that 
an exceedingly surprising answer has been given to this 
important question. From Kowalewsky’s investigations, 
published in 1867, on the individual development of the 
Amphioxus and the adhering Sea-squirts (Ascidia) belonging 
to the class of mantled animals (Tunicata), it has been proved 
that the ontogenies of these two entirely different looking 
animal-forms agree in the first stage of development in a 
most remarkable manner. The freely swimming larve of the 
