ESTERLY: EUCALANUS. 49 
somes, or rhabdome-iike bodies, and the manner of innervation 
(the cells are not inverted) are slag evidence along the same line. 
But the facts at hand do not warrant an extended discussion of this 
matter, nor at the present time more than a reference to the possibility 
of such a relation. 
The more or less prevalent opinions as to the relation existing be- 
tween the median eyes of the Crustacea and the eyes of lower forms, 
such as flatworms, have been referred to previously. And it has been 
shown, that, so far as the conditions in Eucalanus may be taken as 
indicative, the reference of the median eye to those of flatworms, for 
example, is not warranted. On the other hand, the organs of Claus 
are believed to be in every essential point comparable to the inverted 
eyes of other invertebrates, more particularly to those of the annelids; 
vet they exhibit a close similarity in the structure of their cells to the 
median eye. 
It cannot be maintained that a single character, such as the struc- 
ture of visual cells, may in itself be reasonably regarded as showing 
racial affinity. Yet the facts that the cells of the organs of Claus in 
Eucalanus are probably eyes and if so are of the inverted, subepithelial 
type, seem to me to be evidence, along unsuspected lines, of the deriva- 
tion of crustacean from annelidan stock, which as already mentioned, 
has been rather generally, and on other grounds, looked upon as 
probable (Lang, ’88-94, p. 419). The character of the nerve-ter- 
minations as such in the visual cells does not seem to me to be of 
as fundamental importance as the other matters I have referred to. 
I think it probable that even in the organs of Claus the neurofibrillae 
are not in the form of a “‘Stiftchensaum,” but the observations are ' 
not based upon as clear conditions as in the cells of the median eye. 
Whether a visual cell is inverted or not has always been regarded as 
of wide significance, and when cells are met with that possess this 
character, such as those of the organ of Claus, the meaning is worthy 
of consideration. As regards the derivation of the visual organs of 
one group of animals from those of another, Carriére ('85, p. 201) 
is of opinion that all known facts are against it, and that, on the con- 
trary, the visual organs are ‘‘convergent: structures.” Hesse (:02, 
p. 648) says, with regard to Carriére’s idea: ‘‘Wir k6nnen diesen 
Aiisserungen nach dem Vorhergehenden unméglich beistimmen’’; fur- 
ther (Hesse, :02, p. 646) “Dass aber gegeniiber anderen Organen die 
Sehorgane eine Ausnahmestellung einnihmen, derart, dass sie weinger 
von einer Gruppe zur anderen vererbt wiirden (Carriére), muss auf 
Grund der Thatsachen durchaus bestritten werden.” But at the 
