46 THE ANCESTRY OF VERTEBRATES 



dilated. The ciliated pits here arise at the dorsal edge of 

 the little apical plate, a considerable distance in front of 

 the prototroch. 



Homology of olfactory pits of Protostomians and Craniates. — 

 This situation of the ciliated pits in Annelids on the dorsal 

 side of the prostomium corresponds to the ventral side of 

 the prostomium of Chordates, where we find just such a 

 pair of ciliated pits, the olfactory grooves. It seems hardly 

 possible to deny the weight of this complete agreement 

 not only in their function and mode of origin, as 

 observed by Kepner and CASH (1915), but also, as appears 

 now, in their situation. Especially in connection with 

 our results for the optic and auditory organs, the conclu- 

 sion seems inevitable that the olfactory organs of Craniates 

 must also be derived from the corresponding organs in 

 Annelids. 



Three main sense-organs inherited from Annelids, — Thus 

 the rudiments of the three principal sense-organs of the 

 Craniate head are older than the Vertebrate stock itself 

 and have been inherited from the Annelids. During the 

 preparation of the present second publication on my 

 theory, five years after I had first worked it out, I was 

 pleased to find that the same idea, as well as so many others 

 at which I arrived, has been anticipated, indeed has been 

 already put forward, though very shortly and cursorily, by 

 HATSCHEK in the year 1878 (p. 116). He has never 

 reverted to it and soon afterwards seems to have abandoned 

 the idea of an Annelidan origin of Vertebrates ^) and to 

 have adopted a quite different conception of the origin 

 of the Craniate fore-brain (cf. p. 36). His suggestions, 

 however, so closely approach my own results that I will 

 quote them here in extenso, and add the figure which 

 served to illustrate them (fig. 14). 



"Die Scheitelplatte", says HATSCHEK, "und die Anlage der 

 Schlundcommissur der Anneliden ist, unserer Ansicht nach, 

 dem vordersten Theile der Medullarplatte, aus welchem 

 sich .das Gehirn der Wirbelthiere entwickelt, homolog. 



^) In 1911 at least Hatschek declares that the first view of an 

 Amphioxus-embryo, fished in the Pantano, as a living argument "alle 

 meine friiheren Vorstellungen der Annelidenverwandtschaft der 

 Wirbeltiere im ersten Moment hinwegfegte". 



