318 ARTHUR WTLLEY. 



of the Ascidians, I shall have to make a nearlj' complete volte- 

 face from my previous position (32^ pp. 217 — 222) in regard to 

 the homologies existing between the various organs of the . 

 Ascidians and Amphioxus. It was chiefly the position of the 

 endostyle in the larva of Amphioxus, seeming as it did to cor- 

 respond so closely to the requirements of van Beneden and 

 Julin, which led me at first to place unbounded confidence 

 in their results. Singular to say, it is, to a large extent, that 

 very position of the endostyle which now leads me to conclu- 

 sions diametrically opposed to theirs. 



Before proceeding to the description of my observations, I 

 must express my deep sense of the obligation I am under to 

 my master. Professor E. Eay Lankester, to whose counsel and 

 assistance I owe the possibility of pursuing these studies. 



I also have the greatest pleasure in acknowledging the many 

 kindnesses I received from Drs. Dohrn, Eisig, Paul Mayer, 

 and Schiemenz, and Signor Lo Bianco. 



Methods of Obtaining and Preserving 

 Material. 



The embryos of Ciona intestinalis can be obtained in 

 unlimited quantity by artificial fertilisation. It is sufficient 

 to open an adult from the right side, cut across the oviduct 

 and vas deferens, having previously noticed that the former 

 contained ova, and then collect the ova and spermatozoa as 

 they pass out from the point of incision with a glass tube, and 

 transfer them to a glass containing fresh sea water, and mix 

 them well, but gently, together by stirring. Gradually the 

 ova sink to the bottom of the glass, and in about an hour after 

 the above operation they commence to segment. 



After some twenty-four hours the water in the glass is seen 

 to be crowded with myriads of tadpoles swimming about, the 

 mass of them being nearer the surface of the water. Again, 

 after a few hours the tadpoles are no more to be seen, but if 

 the glass be held in the proper light, the surface of the water 

 is found to be covered with greyish patches, which, on exa- 

 mination, turn out to be nothing else than scores of larvse 



