AN ASCIDIAN FOUND AT THE LAND'S END. 113 



attaches itself by its anterior suckers to some solid object, and be- 

 comes permanently fixed. The muscular portion of the tail and of 

 the anterior projections becomes absorbed into the general body- 

 substance, as a tadpole's tail does ; the structureless test of the tail 

 becomes detached, either whole or in pieces ; and the body develops 

 into a mature Ascidian. 



I may remind you that the special interest of the Ascidian-larva 

 lies in the tail, as many biologists of the greatest eminence have 

 considered that the central axial rod of which I have spoken is 

 neither more nor less than the lowest representative of the chorda 

 dorsalis of Vertebrates. It has been stated to resemble the 

 notochord in giving insertion by its sheath to muscles, which are 

 said to hold a position with regard to the nervous system similar to 

 those of the Vertebrata. The nervous system has been stated to 

 be developed in a dorsal cavity, as in Vertebrates, and to be 

 divided by the axial rod from the viceral canal below. The 

 radiating structure of the terminal portion of the caudal test has 

 been compared to the rays in the tails of young fishes, and the 

 perforated branchial sac to the perforated and dilated pharynx 

 of Amphioxus. These views have been strongly held by 

 Kowalewsky * and KupfTer, f and for these reasons among 

 others, they, and many able naturalists and anatomists 

 have held that the Ascidians are more closely allied to 

 the Vertebrata than any of the remaining forms of invertebrate 

 animals. These views have been denied, either in whole or in part, 

 by men of such attainments as Mecznikow, Giard, | Von Baer § 

 and others, and the points must probably be considered unsettled, 

 and I do not wish to express any opinion upon them ; but certainly 

 the fact that many of the highest authorities have considered 

 the Ascidian-larvee as the allies of the lower Vertebrates lends 

 great additional interest to those minute creatures, and the peculiari- 

 ties of structure which have been thought worthy of prolonged and 



* " Die Entwickelungsgeschichte der einfachen Ascidien/' " Mem, de 

 l'Acad. Imp. des sci. de St. Petersbourg." 1866. 



f " Die Staramverwandschaft zwischen Ascidien und Wirbelthiere." 

 " Schultze's Archiv fur Mic. Anat." 1870. 



\ " Etude critique des travaux d'einbryogenie relatifs a la parente des 

 Vertebres et des Tuniciers." " Lacaze-Duthier's Archives de Zoologie." 

 1872. 



§ " Entwickelt sich die Larve der einfacben Ascidien in der ersten Zeit 

 nacb dem Typus der Wirbelthiere ? " " Mem. de l'Akad. Imp. des sci, de 

 St. Petersbourg." 1873. 



