159 | 
present have no concern in the removal of the sexual products, which 
in the female are carried away by a Müllerian duct, whose ostium 
abdominale is a persistent portion of the pronephros. 
We have here as sharp a contrast between the two divisions of 
the Ichthyopsida as was found to obtain in the case of the fore-brain. 
I doubt not that other characters, showing just as marked differ- 
ences, could be found. 
The points just dealt with, i. e. the condition of the fore-brain 
region, and the morphology of the pronephros, appear to me to be 
amply sufficient to justify the contention that the placing of these six 
sub-classes in an ancestral line is opposed to the facts of morphology 
on which it is supposed to be based. 
It would be as false to derive the Selachii from the Cyclo- 
stomata as the Ganoidei from the Selachii, or the Dipnoi 
from Ganoidei. 
Many points requiring discussion occur to me as the result of 
these conclusions, Their consideration would take up so much space, 
and would be all the better for postponement until the publication of 
my memoir on the Ganoidei, that I hesitate to mention them. 
I claim, however, the right to a few words now. 
Many facts lead to the conclusion that the Ganoidei, Se- 
lachii and Dipnoi are not derivable in any way from one another, 
that their ancestors were in all probability Ganoidei, Selachii 
and Dipnoi at a period antecedent to the oldest fossil-bearing rocks, 
and certainly before the Silurian period !). 
The ancestors of the Dipnoi were certainly allied to those of 
the Selachians, but I hesitate to affirm that they were identical with 
them. I must also insist that the Ganoidei did not originate from 
the Selachian ancestors of modern Selachii, nor did the Dipnoi 
arise from the Ganoidei of any period. 
1) Lreın says we must not „assume too hastily that the point 
which our retrospect may have reached at the present moment can be 
regarded as fixing the date of the first introduction of any one class 
of beings on the earth‘ (Elements of Geology, 2"! Ed. 1874). 
(Schluß folgt.) 
