IV 



Those who have read the book to the end will admit 

 that this theory, to say the least of it, merits earnest 

 consideration. They will admit that, unlike most other 

 similar theories, it not only serves to explain known facts 

 but that also its application has advanced us further in 

 several respects. Of these I will mention here only the 

 problem of the hypoglossus and its relation to the gill-slits 

 and the cranium (cf. Plate 1), and the results given in the 

 last chapter. 



In the treating of the different problems, I have tried 

 each time to give the reader first an idea of the divergent 

 opinions and the confusion often prevailing. Though this 

 does not make the reading of the book easier and more 

 agreeable — problems having been made often much more 

 complicated by the investigatcis than they are in reality — 

 I have thought it advisable to do so in order to emphasize 

 the value of a means of escaping from this confusion. 



The expressing of a persons thoughts correctly in a 

 foreign language is no easy matter, I am greatly indebted, 

 therefore, to Mr. HUMPHREYS, officer of the Royal Flying 

 Corps who was interned in The Hague during the year 

 1918, for having gone over with me the whole article, and 

 to Mr. Moon, engineer of Batavia, for having once more 

 reread with me the proofs If in spite of this the English 

 be not yet perfect, I trust that these imperfections, if any, 

 will not give rise to any misunderstandings. 



BATAVIA, March 1922. 

 Laboratory for Marine Investigations. 



H. C. DELSMAN. 



