PROTOSTIGMATA OF MOLGULA MANHATTENSIS. 143 



Seeliger (1885), and Laliille (1890), the rule is that the 

 definite stigmata arise each by separate perforation of the 

 pharyngeal wall. 



A method of formation of the stigmata intermediate in 

 character between that followed by a form like Ciona on 

 the one hand, and Clavelina on the other, is afforded by 

 Bo try 11 us, as shown by Mr. Grarstang, to whose researches 

 I shall again refer. 



Meanwhile I pass on to a brief recapitulation of my pre- 

 vious 



Observations on Cigna intestinalis.^ 



1. Distigmatic Stage. — I could not detect any diifer- 

 ence in the time and manner of formation of the two proto- 

 stiginata which characterise this stage. They appeared to me 

 to arise simultaneously, and to resemble one another in all 

 respects. Accordingly, to account for this similarity and 

 simultaneity, I suggested a certain interpretation (namely, the 

 precocious subdivision of a single branchial pouch) which I do 

 not relinquish, but do not now wish to press further. 



In a recent publication Professor Julin^ dissents from my 

 version of affairs regarding this stage. As he reserves full 

 details for a future occasion it is not desirable to enter upon 

 an extended discussion, and I will only touch upon one point. 

 M. Julin states definitely that the stage now under considera- 

 tion is preceded by a stage in which only one pair of primary 

 stigmata is present ; in other words, that the two pairs of 

 stigmata which characterise this stage do not arise simul- 

 taneously, but one after the other. 



These two pairs of stigmata arise before the change of axis 

 of the body of the larva (which ensues after fixation) has 



^ See this Journal, vol.34, January, 1893, p. 317; also in ' Proc. Roy. 

 Soc.,' vol. li, 1892, p. 513. 



2 Charles Jiiliu, 1899, "Contribution a I'histoire phylogenetique des 

 Tuniciers ;" " lleclierches sur le develop|)ement du pericarde, du cceur, et les 

 transformations de I'epicarde chez les Ascidies simples;" ' Miscellanees 

 biologiques,' Trav. Stat. Zool. Wimereaux, t. vii, see p. 33(5. 



