of doliola takes place as in the larvae of ascidians . In 

 the latter the disappearance of the tail was noticed for the 

 first time by Milne-Edwards in an example of the colonial 

 ascidian Amouruoium proliferum, and was described in more 

 detail by Krohn for Phallus-La mammillata . 



The metamorphosis of doliola was again studied by Krohn 

 on the species Doliolum Nordmanni. Krohn represented two 

 stages of transformation; Figure 47, A represents the stage 

 when the tail of the larva has not begun reduction; and 

 Figure 47, B, the larva with shortened tail. Until metamor- 

 phosis the tail of the larva is tapered, with the two ends 

 covered with gelatinous membrane a_; its axis d_ is composed 

 of cuboidal cells situated in one row, so that it seems to 

 be segmented. The root of this axial shaft penetrates into 

 "the vesicular appendix" c_, lying under the digestive tract 

 of the larva. This vesicle decreased simultaneously with the 

 reduction of the tail and at the end it disappears (139) . In 

 the stage represented in Figure 47, B, all organs in the 

 larva are already differentiated; on its dorsal side there is 

 the placing of the stolon £. 



Krohn ! s description of the structure of the larva of 

 doliolum and its transformation distinctly shows that he saw 

 in it all the principal features of organization, on the basis 

 of which the doliolum was later counted as a type of chordate 

 (subtype tunicate, class salpa) : the presence of the reduced 

 cord at the time of metamorphosis ("axis of tail"), the situa- 

 tion of the nervous ganglion o_ on the dorsal side and the 

 heart m on the ventral side. 



Correct evaluation of Krohn ! s investigations was given 

 by V. N. Ulianin in the classic monograph on doliola, first 

 published in Russian, and two years later in German.' 7 ** Ulianin 

 wrote the following: "Soon after the appearance of Huxley's 

 article the doliolum was found in the Mediterranean by Krohn. 



78. V. Ulianin, ON THE DEVELOPMENT AND REPRODUCTION OF 

 DOLIOLUM (Moscow, 1882), 100 pp. B. Uljanin, DIE ARTEN 

 DER GATTUNG DOLIOLUM IM GOLFE VON NEAPEL UND DEN 

 ANGRENZENDEN MEERABSCHNITTEN, FAUNA UND FLORA 

 D. GOLFES V. NEAPEL, X. Monographie (1884), 140 pp. 



588 



