ORGANIZATION AND GROWTH 



217 



FIG. 57. 



&c). This occurs no matter whether the oral or the anal tube 

 is incised. Fig. 55 illustrates such a case; an incision 

 was made into the oral tube; a week later ocellse had 

 formed along both edges of the wound. The foot is not 

 indicated in the drawing. Ciona intestinalis, therefore, 

 behaves not so much as Cerianthus, but 

 more like certain Hydroids, in which we 

 have to assume a movement of formative 

 substances in two directions. I do not 

 think that anyone will be inclined to 

 believe that the general causes underly- 

 ing the formation of organs are deter- 

 mined by the position which the animal 

 occupies in the animal scale. 

 2. I have still to describe what occurs after the ocellse are 

 formed. All the elements of the cut edge begin to grow in 

 length, and a new tube springs from the cut edge. The ani- 

 mal of Fig. 55 had assumed the form 

 shown in Fig. 57 four weeks later. A new 

 third tube had been formed at a. This 

 continued to grow in length, and attained 

 not only the size of the normal tube, but 

 usually became even longer than this. 1 



If* several incisions are made simulta- 

 neously into the same animal, several new 

 tubes may be formed at once. The ani- 

 mal in Fig. 58 has four such tubes. 



VII. EXTIRPATION AND REGENERATION OF THE CENTRAL 

 NERVOUS SYSTEM IN CIONA INTESTINALIS 



1. Much more remarkable than that just described is 

 another phenomenon of regeneration in this animal namely, 



i Dr. P. Mingazzini made experiments upon Ciona intestinalis similar to those 

 which I have described, and also found that a third tube is formed when the mantle 

 of Ciona is incised. While at work upon paper vi I obtained his published account 

 of these experiments: ?. MINGAZZINI, Bolletino della Societd, di Naturalisti 

 (Napoli, 1891). 



FIG. 58 



