1909] 1,'ilhr: Halocynthia johnsoni a. sp. 79 



which it has hitherto held as adequate and has used without 

 particular questioning. It is sure to break up, so to speak, cer- 

 tain of its observations en massi into elements which must be 

 examined more in particular. An excellent special instance of 

 (his general principle is afforded by the very matter of ascidian 

 structure and classification here encountered. Recenl studies by 

 Selys-Longehamps (1899), by Longchamps el Damas (1900), and 

 by Damas alone (1900). are even more strikingly to the point so 

 far as actual observation goes, than are mine. For the present pur- 

 pose I make reference to Damas's work chiefly. Concerning the 

 multiplication of branchial stigmata Damas says: "('"est I'opin- 

 ion ancieime sur le mode de formation des stimulates definitifs 

 qu'un recent ouvrage theorique resume ainsi : 'Dans la branchie, 

 le Dombre des fentes stigmatiques et des tremas s'accroit, mais 

 sans ordre" (p. 20). By reference to the studies of Willey, 

 Selys-Longchamps and others, he shows how erroneous the notion 

 is that the production of new stigmata is 'sans ordre.' And he 

 himself not only confirms the residts of others as to the origin 

 of new stigmata from those already existing, but goes a long step 

 further by showing the extent to which the formation of various 

 oilier elements of the branchial sac is correlated with the forma- 

 tion of new stigmata. Without entering into the details of his 

 interesting study, the purport of it. so far as concerns this par- 

 ticular point, is contained in the following: "Les lois de nombre 

 et de position qui regissent les differents ordres distingues plus 

 haut de sinus transverses, de languettes dorsales et de muscles — 

 lois de redoublement et d'alternance par intercalation — sont la 

 consequence immediate et un autre mode d 'expression du devel- 

 oppement de ces differents elements" (p. 29). The "develop- 

 ment of the different elements" on which the "law of number 

 and position" depends in Ciona intestinalis, the particular species 

 studied by Damas. consists in the formation of six protostigmata 

 in the larva, each of which gives rise to a primary series of de- 

 finitive stigmata, these series being- separated by five primary 

 inli rs( rial sinuses, and then the division of each of these pri- 

 mary series by secondary sinuses, and so on. But as indicated 

 in the law quoted, the multiplication of the dorsal languets and 

 of the muscle bands is intimately correlated with the multiplica- 

 tion of the other branchial parts. 



