Morse.] 354 [October 18, 



in a series of short, cylindrical masses. Lowig and Kolliker 1 repre- 

 sent the tail of a larval Botryllus with the segments divided in a 

 median line, making a double row of segments running parallel, as 

 well as a double row of smaller cells representing the investing mem- 

 branes. This condition may represent a later stage, though all the 

 specimens preserved by Mr. Gavit present this peculiar appearance. 



With the breaking up of the segments, a contraction of the axis has 

 taken place at the tail, leaving a distinct cavity, this is more plainly 

 shown in fig. 5, where double transverse lines are faintly seen indi- 

 cating the former presence and position of the segments. The fin is 

 seen as a continuous membrane bordering the entire outline of the 

 animal. The fin rays are very conspicuous and commence just at 

 the junction of the tail with the body and start off at right angles 

 with the longitudinal axis. At the tail they rapidly diverge and 

 finally run parallel with the axis. The wider marks of the fin rays 

 correspond nearly in number to the number of segments in the axis. 

 As these were invisible in the living specimens it is impossible to say 

 whether they agree as to number and position with the segments. 



In conclusion it is interesting to add that Savigny, Milne Edwards, 

 Van Beneden, Sars, Kolliker, Dalyell, Agfrssiz and many others 

 have added their testimony in regard to the existence in many gen- 

 era of Ascidians of active tailed larvae, till it was supposed that this 

 appearance of the embryo was characteristic of all Ascidians. 



Lacaze Duthiers, 2 however, describes the young of Molgula as pre- 

 senting a remarkable exception ; the young not having a tail, nor 

 showing any signs of activity, but escaping from the egg with the 

 appearance of Amoeba, by flowing out of the egg, a rounded plastic 

 fluid mass, and remaining sedentary at the bottom of the vessel. 

 Albany Hancock 3 on the contrary has observed the embryos of two 

 species of Molgula in which they present all the features of the usual 

 active tailed larvae, and questions whether Lacaze Duthiers had Mol- 

 gula at all; for certain reasons, which he presents, he thinks Duthiers, 

 had another genus, Eugyra, under examination. Prof. A. E. Verrill 

 however, in a series of valuable papers on the Ascidians of New 

 England, 4 states in regard to Lissoclinum tenerum V. (gen. et sp. 

 nov.) that "the eggs are few and relatively very large. The develop- 



1 Annales des Sciences Naturelle, in Series, Tome v, pi. 7. 



2 Comptes Rendus, Tome ixx, p. 1154. 



8 Annals and Magazine Nat. Hist, iv Series, No. xxxv, p. 353. 

 4 American Jour. Science and Arts, Jan. to June 1871, p. 445. 



