Summary of Conclusions Reached 505 



resented in the total yield of petroleum (234,917,043,312 

 gallons) throughout the world up to 1914. Fishes are the 

 only organisms and the only sources from which such an oil 

 and petroleum supply could be obtained. 



With the probable exception of fishes which had mi- 

 grated seaward in the Carboniferous Limestone period, all 

 the earlier oil supplies up to late Jurassic or even early 

 Cretaceous time, were derived from freshwater forms. The 

 researches of Warren-Storer, later of Engler and of Day, 

 clearly prove that all the important petroleum products can 

 be obtained, from fish-oil alone, or from it when heated in 

 presence of lime or wood, or other substances. 



Chapter 3. The evolution of fishes from invertebrates. 



In detailed study of the Metanemertinea and their 

 descendant groups the Hemichordata, Urochordata, Cep- 

 halocordata, and Chordata, comparison is made of the 

 relative size and shape, of the color, of dermal structures 

 including glands, thread cells, dermal scales or plates, and 

 stylet teeth. A review of the sense organs of the head is 

 then made. In study of the mouth and alimentary canal, 

 emphasis is laid on the homology between the attachment 

 line of the proboscis with its sheath in metanemerteans, and 

 the velum or velar membrane of vertebrates. Like em- 

 phasis is laid on the homological continuity of at least a 

 part of the highly glandular mid-oesophagus of metane- 

 merteans, and the endostyle, hypopharyngeal groove, or 

 thyroid gland of chordate animals. Homological continuity 

 of the median forward diverticulum from the gut in metane- 

 merteans, with the similar simple organ that is the liver 

 of Petromyzon and Lepidosteus, and with the bilobed or 

 trilobed liver of higher fishes is indicated. The apparent 

 formation during embryonic life, of the mesoblastic mes- 

 enteries is traced. 



The relations between the parts of the proboscis and 

 proboscis-sheath of Metanemerteans, and the notochord, 

 pituitary body, horny teeth, and associated parts of chor- 

 date animals, are followed out. 



A correlation of two pairs of brain-lobes in metane- 

 merteans, with the corresponding primitive lobes in Dipnoi, 



