10 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



asymmetry observed in so many of the Salpidae may be due to 

 crowding in a biserial stolon. I see no sufficient evidence that the 

 cyclic grouping of the zooids upon the stolon is more archaic than 

 the biserial arrangement, except the fact that it occurs in those species 

 which for other reasons we regard as the most primitive. 



We have even in Cyclosalpa pinnata an interesting bit of asym- 

 metry in the larger eyes of the aggregated individuals, which Met- 

 calf 1 has mentioned. "Goppert 2 points out that in Salpa maxima, 

 in individuals from the right side of the chain, the long axis of the 

 eye is directed obliquely toward the right, while in individuals from 

 the left side of the chain the eye points toward the left. This gives 

 importance to a slight though constant peculiarity I have observed 

 in the otherwise symmetrical eye of the chain Cyclosalpa pinnata, 

 which serves to determine the relation of the animal to the stolon. 

 In this group the individuals stand with both then antero-posterior 

 and dorso-ventral axes at right angles to the [young] stolon. In the 

 large dorsal eye of each individual, on the side distal from the former 

 attached end of the stolon, there is a small unpigmented spot in the 

 midst of the pigment area of the second region of tjie eye." This 

 minute asymmetrical feature is related to the position of the zooid 

 in the at first biserial stolon. Only when the individuals have 

 reached their adult form do they assume the whorl grouping. Even 

 in Cyclosalpa pinnata, therefore, we find a trace of asymmetry in the 

 aggregated form, and this is found to be correlated with the position 

 of the zooids in the stolon in its earlier stages, before the whorls are 

 formed and while the arrangement is that of a double series of indi- 

 viduals, as in the stolons of all the Salpidae except the Cyclosalpae 

 symmetricales. This suggests that the habit of forming whorls at 

 the tip of the stolon in the Cyclosalpae symmetricales is secondary. 



It is in the anatomy and development of the eyes in the aggregated 

 form that we find the clearest evidence of the relatively archaic 

 character of Cyclosalpa pinnata. One familiar with the condition of 

 the eyes in the several species of Salpidae could hardly believe that 

 they show an ascending series culminating in the elaborate and 

 histologically perfect eye of Cyclosalpa pinnata, though in my first 

 papers upon this subject I took this position, which now seems to me 

 so untenable. 3 We seem clearly to be dealing witli a series of 

 increasingly degenerate forms, so far as the structure of the eyes is 

 concerned. This degeneration goes so far that in its most extreme 

 condition one doubts the functional value of the organs affected. 

 Such an imperfect and possibly functionless eye as we find at its 

 worst could hardly be regarded as the starting point of an ascending 



i Metcalf (1S93, c), p. 370. 

 2 Goppert (1892). 



8 Lest it be thought that I may havo been influenced in this former conclusion by my teacher, Prof. W. K . 

 Brooks, I would say that at the time of my writing the former papers he demurred from this opinion. 



