506 



12) The higher sense organs of the Ctjclostomata are all paired, 

 since the nose (i. e. the nasal or olfactive epithelium) exists in the 

 embryo as well as in the adult in the form of two circumscribed areas 

 lying on either side of the median line, each of which receives the 

 entire nerve supply afforded by the olfatory nerve of its side. 



1 3) The parietal-pineal eye of the Ctj do stornata and other verte- 

 brates has been developed from a median portion of the pigmented eye 

 of Amphioxus. The rudiments of this eye were derived from (segmen- 

 tal) sense organs; but the eye itself is never developed from two right 

 and left halvei^. in so far as the closure of the medullary folds would 

 necessitate this. 



14) The neural axis of all vertebrates is coextensive with that of 

 the chorda or vice versa, since the neural axis is phylogenetically as 

 well as ontogenetically the older structure. 



15) The pituitary prominence of the skulls of vertebrate does not 

 mark a fixed point in the axis of the vertebrate body, as the relation 

 of the anterior end of the chorda and of the hypophysial organs clearly 

 proove. 



1 6) In the discussion of the segmentation of the head it has be- 

 come necessary to deny any segmental value whatsoever to any portion 

 of the Chondro- or ossi-cranium. They have no greater value than the 

 intestine and all apparent segmental characters have been impressed 

 upon them by other organs of a segmental nature. 



17) The headcavities or spaces included within the mesoblastic 

 somites occurring in the head region possess relatively the greatest im- 

 portance in an acraniate stage before a skull or anything comparable 

 with a primordial cranium has made its appearance. This is true from 

 the ontogenetic as well as the phylogenetic standpoint. 



18) The hypophysis is a structure which arose in the vertebrate 

 phylum long after the chorda was established, as Amphioxus prooves, 

 and was connected in an important way with the infundibulum. It 

 arose as an organ of taste and the infundibulum was its nerve. 



19) The optic chiasm (the trochlear chiasm as well) has arisen 

 within the vertebrate group above the Amphioxus condition. 



20) The explanation of the increased number of gill slits of Am- 

 phioxus over those of other vertebrates (which certainly show traces of 

 considerable reduction in number) is to be found in the habits of Am- 

 phioxus, which is not a free swimming animal an cannot be a predatory 

 one. It depends for its food upon the size and power of its branchial 

 apparatus to create currents and keep moving a sufficient volume of 

 water to supply it with the requisite amount of food which is contained 

 in only limited quantities therin. 



