1913.] 



On the Origin of the Ascidian Mouth. 



459 



These groups also form a series with reference to the amount of rotation 

 of these organs around the anterior end of the body. In the Tunicate they 

 are all dorsal. In the Cephalochordate they are all dorsal except the last. In 

 the Vertebrate the last two are ordinarily ventral and exceptionally nearly 

 all of them may come to the ventral side. 



It may be noticed that the condition in the Tunicate strongly supports the 

 view that the neural tube was originally not nervous but a part of the digestive 

 system. 



I hope shortly to publish a more extended account of the later embryonic 

 development of the Ascidian. I wish to express here my appreciation of the 

 splendid facilities for research and for the collection of material which were 

 placed at my disposal by the Biological Board of Canada, both at the Atlantic 

 Station, St. Andrews, New Brunswick, and at the Pacific Station, Departure 

 Bay, British Columbia. My material was obtained at these stations. 



LITERATURE REFERENCES. 



1871. A. Kowalevsky, " Weitere Studien liber die Entwickelung der einfachen 



Ascidien," ' Arch. Mikr. Anat.,' vol. 7, p. 101. 

 1870. C. Kupffer, " Die Stammverwandtschaft zwiscken Ascidien und Wirbelthieren. 



Nach Untersuchungen iiber die Entwicklung der Ascidia canina (Zool. Dan.)," 



' Arch. Mikr. Anat.,' vol. 6, p. 115. 

 1904. O. Seeliger, "Tunicata" in Bronn's ' Kl. u. Ordn. Tier-reichs,' Lf. 48-52. 

 1893. A. Willey, " Studies on the Protochordata, II," ' Quart. Journ. Micr. Sci.,' vol. 35, 



p. 295. 



VOL. LXXXVI. — B. 



