191^] Ix'iiter-Forsijth: Ascidians of Southern Calif ornia 451 



valleys. A cross-section of the ridges reveals, even to cursory inspec- 

 tion, the fact that the outer half, approximately, of the test-substance 

 of the ridge is denser and more opaque than the inner part. This ease 

 of sharp differentiation within the mass of a structure produced 

 mainly by secretion should repay investigation. 



Particular attention may be called to the fact so clearly brought 

 out in the table, that the number of inner longitudinal vessels of the 

 branchial sac, both on and between the folds, increases regularly and 

 continuously with the increase in size, and hence presumably with the 

 age of the animals. 



Equally clear is it that the branchial tentacles also increase in 

 number. This result corresponds with what was found by Ritter 

 (1913) in several other species, but it is interesting to notice that 

 certain differences in the mode of increase of parts in different species 

 is indicated. For example, while the addition of new branchial ten- 

 tacles in S. montereyensis is obvious for a large portion, at least, of 

 the individual's life, this seems to be rather exceptional; for little or 

 no increase in number occurs in Halocynfhia anrantium. Boltcnia 

 ovifcra, and Styela macrenteron, species previou.sly studied with refer- 

 ence to the same point. 



Although the three stalked species of Styda occurring on the 

 Pacific Coast of North America are well known to the senior author 

 of this paper, two of them, S. grceleyi and S. yacutatensis having been 

 described by him, until recently there has been some doubt in his mind 

 about the specific distinctness of the three. But the studies of Hunts- 

 man and our own have removed the doubt. 



It is noteworthy that this species, like several other ascidians, 

 seems to flourish much better on the piles and other similar objects 

 introduced into the water than on the natural shore rocks. The senior 

 author has collected S. montereyensis from many points on the coast 

 from San Diego to ilendocino, but has never seen a specimen of any- 

 thing like maximum size growing on native rocks. The largest indi- 

 viduals seen were on the piles of the wharf at Santa Barbara ; and at 

 no other point has it been found in such abundance as there. How- 

 ever, it occurs in abundance and large size on the wharfs and break- 

 waters in the vicinity of Los Angeles. 



