182 



THE ORIGIN OF VERTEBRATES 





I do not know how to decide the question which thus arises. 

 Supposing, for the sake of argument, that this column of fat-cells 

 has really taken the place of the original dorsal heart, what criterion 

 would there he as to this ? The heart ex hypothesi having ceased to 



function, the muscular tissue 

 would not remain, and the 

 space would he filled up, 

 presumably with some form 

 of connective tissue. As 

 likely as not, the connective 

 tissue might take the form 

 of fatty tissue, the storage 

 of fat being a physiological 

 necessity to an animal, while 

 at the same time no special 

 organ has been developed 

 for such a purpose, but fat 

 is being laid down in all 

 manner of places in the 

 body. 



This dorsal fat-column, 

 as it is seen in Ammoccetes, 

 is not found in the higher 

 vertebrates, so that it pos- 

 sesses, at all events, the 

 significance of being a pecu- 

 liarity of ancient times 

 before the vertebrate skele- 

 tal column was formed. 



I mention it here in 

 connection with my view 



Fig. 73. — Section through the Notochord 

 (nc), the Spinal Canal and the Fat- 

 column (/.), of Ammoccetes, drawn from 

 an Osmic Preparation. 



sp. c, spinal cord; gl., glandular tissue filling 

 the spinal canal; sk., Gegenbaur's skeleto- 

 genous cells ; p., pigment. 



as to the origin of verte- 



brates, because there it is, 

 in the very place where the 

 dorsal heart ought to have been. For my own part, I should not have 

 expected that a muscular organ such as the heart would leave any 

 trace of itself if it disappeared, so that its absence in the dorsal region 

 of the vertebrate does not seem to me in the slightest degree to 

 invalidate my theory. 



