1876.] The Vertebrates and Invertebrates. 601 
new one, homologous with the nasal passage of Myzine. Thus 
wecan explain the astonishing fact that the mouth-opening of 
the Ascidian larva has a communication with the fore-wall of the 
so-called cerebral vesicle. It is the last vestige of the openings 
in the nasal sacs by which the olfactory nerves entered. 
The most patent objection to Dr. Dohrn’s view about Amphi- 
oxus is that it fails to account for the development of a many- 
segmented respiratory apparatus as a degeneration from a higher 
animal with a small number of gill-arches. It would appear far 
more reasonable to suppose Amphioxus to be a degeneration from 
amuch lower elevation than the cyclostome type, namely, from 
some stage where the respiratory apparatus retained the multi- 
serial character derived from its Annelid forefathers. 
The key-note of the author’s reasonings is to be found in the 
principle of transformation of function (Functionswechsel), on 
which he lays great stress. He states it as follows: The trans- 
formation of an organ happens through a succession of functions 
being discharged by one and the same organ. Each function is 
à resultant of several components, of which one constitutes the 
chief or primary function, while the others are lower or secondary 
functions, Diminution of the importance of the chief function 
with increase of the importance of a secondary function alters 
the entire resultant function ; the secondary gradually rises to 
the chief function, the resultant function becomes different, 
and the consequence of the whole process is the transformation 
of the organ. This principle is considered to be a complete an- 
Swer to the difficulty so strongly insisted on by Mr. Mivart, the 
neompetency of natural selection to account for the incipient 
Stages of subsequently useful structures. Dr. Dohrn’s statement 
of his principle does not strike us as very different from Mr. 
ttwin’s (Origin of Species, fifth edition, page 251), though a 
Tittle more definitely stated. Mr. Darwin says, ‘The sume 
“gan having performed simultaneously very different functions, 
- and then having been in part or in whole specialized for one 
= 0n; and two distinct organs having performed at the same 
es e the same function, the one having been perfected whilst 
Q sont the other, must often have largely facilitated eae 
is The illustrations given by Dr. Dohrn of the steps y 
: z the anterior extremities of crustacea became applied to 
mastication, how the mouth of vertebrates originated from a pair 
£? gill-clefts, how the respiratory apparatus of tunicates ea a 
~~ ‘tom that of vertebrates, etc., are, however, exceedingly 
‘esting, 
