928 The American Naturalist. [November, 
hitherto found little favor. Nevertheless, I hold that Amphi- 
oxus is more closely related to the Tunicates than to the Ver- 
tebrates, and that we ought to establish a group, which might 
be named Atriozoa,and would comprise Amphioxus and Tun- 
icata. 
The systematic value of embryology has been hitherto little 
recognized, but it certainly is of the greatest significance. It 
is not true that embryos are alike; on the contrary they show 
class, ordinal and generic differences from one another. I 
think, therefore, great stress must be laid upon the very close 
similarity in the embryonic development of Amphioxus and 
Tunicates. The fact of this similarity is now so familiar that 
it is superfluous to dwell upon it. On the other hand, it is 
desirable to renew attention to the large factor, which inter- 
pretation becomes, as soon as we attempt to establish a similar- 
ity between the ontogeny of Amphioxus and of the Verte- 
brates. 
As regards the adult organization. The entire absence of 
lateral eyes and of lateral ears sharply separates both Tuni- 
cates and Amphioxus from the Vertebrata, while in the sense 
_ organs, they do possess, namely, the pigment spot or so-called 
eye, and the so-called olfactory pit, they are closely similar to 
one another, and quite unlike vertebrates. The attempt to 
identify the eye of Amphioxus with the pineal eye rests upon 
sheer speculation, and assumes that an organ developed in 
front of the neuropore is identical with one developed behind 
it. As regards the “olfactory pit,” Kupffer’s attempt to 
demonstrate a lobus olfactorius impar in Vertebrates is ob- 
viously unsuccessful. The atrium is another feature common 
to the Atriozoa, and is so highly distinctive, that it affords, 
what seems to me, an appropriate name for the whole group. 
The differences in the development of the atrium in the two 
classes of the Atriozoa are not, it is generally believed, such as 
to upset the homology, which is commonly maintained. The 
pharynx with its endostyle and ciliated bands, shows almost 
identity in Tunicates and Amphioxus, but only remoter 
resemblance to the Vertebrate pharynx, even to that of Am- 
mocoetes with its hypobranchial groove. The gill clefts of 
