528 
Appendicularia, if anywhere, that we find conditions which justify com- 
parison with the vertebrates‘). 
But even the eye of the ascidian tadpole has apparently little 
significance in connection with the ancestral condition of the eyes of 
vertebrates. The condition in Amphioxus, with metamerized paired 
groups of bicellular eyes in the nerve cord, and the condition in the 
early embryos of many vertebrates in whose medullary plates are 
found metamerized pairs of shallow pits from three of which pairs 
optic organs later either form or begin to form, seems in many ways 
more primitive than that in the ascidian tadpole in which but a single 
asymmetrically placed optic pit is found in the sensory vesicle. 
It may not unlikely be true that the condition with a single 
anterior enlargement of the central nerve tube is ancestral (cf. Am- 
phioxus and the tunicate tadpole). It may well be true that one or 
more light-perceiving organs were associated with this vesicle. But 
to attempt to draw phylogenetic conclusions from the details of the 
anatomy of the eye of the ascidian tadpole would hardly be safe. 
Surely, then, to argue from the condition of the eyes of Salpa, and 
especially of the chain form of Salpa, as to the phylogeny of the eyes 
of vertebrates is entirely unwarranted. 
One important error that lies back of all such attempts is the 
failure to realize that Salpa has apparently been derived from a sessile 
ancestor somewhat like the adult ascidian, and not from a form like 
Appendicularia. Nearly all features of Salpa’s anatomy and many 
features of its embryology point to this conclusion, and none more 
clearly than the condition and development of its central nervous 
system. Comparison with Doliolum and Pyrosoma confirms this view. 
I have elsewhere shown that Octacnemus?) is not related to Salpa, but 
rather to the most primitive of the ascidians, the Clavelinidae, so it 
cannot give evidence upon this point. 
Würzburg, Oct. 10th, 1906. 
1) Some years ago I made somewhat similar comments upon 
Bwutscuurs brief paper in which from his description of the eyes of 
Salpa he drew conclusions as to the phylogeny of the eyes of verte- 
brates. Cf. O. BürscHLı, Einige Bemerkungen über die Augen der 
Salpen, in Zool. Anz., Bd. 15, 1892, and M. M. MrrcArr, On the Eye, Sub- 
neural Gland, and Central Nervous System, in Zool. Anz., Bd. 16, 1893. 
2) M. M. Mercautr, Notes upon an apparently new Species of 
Octacnemus, a Deep Sea, Salpa like Tunicate, in: Johns Hopkins Univ. 
Cire., Vol. 12, 1893; also Notes on the Morphology of the Tunicata, 
in: Zool. Jahrb., Abt. Morphol., Bd. 13, 1900. 
