ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



629 



With regard to the homoh:igies of the most important organs of 

 the Tunicata, the following useful table is given : — 



Dr. Sceliger regards the Vertebrata and Tunicata as being two 

 separate branches derived from a common root-form ; whatever be 

 the real position of Amphioxtis, it cannot, ho thinks, bo regarded 

 as the bond of connection between the Vertebrata and the Tunicata. 

 The stem-forms may have had close relationships to the segmented 

 worms, and it is even possible that they have several common ances- 

 tors ; in sncli case the nerve-tube of the Tunicate larvoo might be the 

 homologuo of the ventral cord of worms. This view seems to be 

 supported by the discoveries of Hatschek and Kowalcvsky ; but it 

 is to be noted that the gastrula of Ascidians is not completely homo- 

 logous with the primitive form common to all the Mctozoa, inasmuch 

 as it contains the materials of three segments, derived by a double 

 gemmation from the primitive one. 



Ser. 2.— Vol. V. 2 T 



