1897.] Cephalic Homologies. 937 
3. Excretory organs.—Boveri has shown that the excretory 
organs of Amphioxus are tubules which begin with a ciliated 
internal funnel and open through the ectoderm, and that their 
primitive arrangement is probably segmental]; they are confined 
to the branchiate region. They differ, therefore, from the seg- 
mental organs of Vertebrates, which open into a longitudinal 
internal duct, and occur only behind the branchiate region. 
It is true that the attempt has been made to show that the 
duct is originally derived from the ectoderm, but the weight 
of evidence—see especially Price on Bdellostoma, and Rabl 
on Elasmobranchs—is at present against this view and in favor 
of the mesothelial origin of the duct. In Annelids segmental 
organs have the same arrangement as in Amphioxus, they 
open directly through the ectoderm, and they also may occur 
in that part of the body which, on the theory of Annelid an- 
cestry, must have been evolved into the pharynx. The mor- 
phology of the excretory organs is thus readily perceived to 
indicate the Annelidian rather than the Vertebrate relation- 
ships of Amphioxus. 
And now I ask, must we not conclude that Amphioxus is a 
Chordate nearly related to Tunicates, more remotely related to 
Vertebrates, and revealing in its organization important dif- 
ferences from other Chordata, which differences demonstrate a 
true kinship with Annelids? Now certainly no one would 
venture to regard Amphioxus as the ancestor of the Annelida, 
hence we are obliged to consider the Annelida as representing 
the ancestral type of the Cephalochorda, and, therefore, of all 
Chordata. 
b. The position of Appendicularia—The conclusion just stated 
involves the assumption, so far as now appears, that Appen- 
dicularia is not an ancestral but a secondary type. But 
Appendicularia much resembles a young stage of other Tuni- 
cates (free swimming larve), and we have learned to trust so 
much to the law of recapitulation (Haeckel’s Biogenetisches 
Grundgesetz) that it is hard to believe that it does not govern 
Appendicularia, which would then be of the phylogenetic sig- 
nificance assumed by W. K. Brooks, whose argumentation is 
so strong, that even while defending the Dohrn-Semper theory, 
one must have in reserve readiness to change sides. 
