THE PROTOCHORDATA. 



2. (p. 273.) On the subject of the praeoral lobe and the api- 

 cal nervous system of Invertebrates, see the following: BALFOUR, 

 F. M. Comparative Embryology. 1881. Vol. II. Chap. 12. 

 Observations on the Ancestral Form of the Chordata. BEARD, 

 J. The Old Mouth and the New, A Study in Vertebrate Mor- 

 phology. Anat. Anz. III. 1888. pp. 15-24. WILSON, E. B. 



The Embryology of the Earthworm. Jour. Morph. III. 1889. 

 pp. 387-462. HATSCHEK, B. Lehrbuch der Zoologie. 3d Liefer- 

 ung. Jena, 1891. WILLEY, A. On the Evolution of the Praoral 

 Lobe. Anat. Anz. IX. 1894. pp. 329-332. 



3. (p. 285.) From what has been said in the text, it is obvious 

 that the hypophysis of the craniate Vertebrates, in becoming 

 separated from the neuropore, has retained (at least in the embryo) 

 its primitive relations with the buccal cavity, and, like the latter, 

 has been made to assume its present position in consequence of 

 the forward growth of the brain and the ensuing cranial flexure. 

 In Amphioxus, the hypophysis (i.e. olfactory pit) arises as an 

 ectodermic involution immediately over the neuropore, but still 

 independent of the latter. In other words, the neuropore exists 

 in Amphioxus for a considerable length of time before the hypoph- 

 ysis forms ; and this is in accordance with what we should expect 

 from the analogy of the craniate Vertebrates. In the Ascidians, 

 however, the conditions are somewhat different, and there is at first 

 no such obvious differentiation between neuropore and hypoph- 

 ysis. For the simple Ascidians (e.g. Ciona) it must at present 

 remain doubtful whether the increase in size of the hypophysis 

 takes place entirely by interstitial growth, or whether there is any 

 ingrowth from the wall of the buccal tube at the lips of the aper- 

 ture (dorsal tubercle) of the hypophysis. In any case there are 

 not wanting indications in the Ascidians of a distinction, and even 

 separation, between the distal portion of the hypophysis, which 

 at first opens into the cerebral vesicle, and the proximal portion, 

 which opens into the buccal cavity. In the adult, the proximal 

 portion of the hypophysis has the form of a simple duct, opening 

 by the so-called dorsal tubercle into the buccal cavity, while the 

 subneural gland arises as a proliferation from the ventral wall of 

 the distal portion. In Phallusia mammillata, as was discovered 

 by JULIN {Archives de Biologie, II. iSSi. pp. 211-232), num- 



