352 WILLIAM PATTEN. 



connected in any way with an alimentary canal. Only a 

 strong faith in enteric diverticula^ and in the red, white, and 

 blue gastrules of embryological treatises, can lead one to 

 believe in the endodermic origin of the notochord. On the 

 other hand, its growth at both ends from superficial cells, and 

 the manner in which it is frequently wedged in between the 

 nerve-cords, indicate its ectodermic origin. 



Owing to the origin of the spinal artery of Scorpio from 

 the interganglionic portions of the median furrow, temporary 

 communications are formed between the central canal and the 

 artery. The communications between the notochord and the 

 neural canal of some Vertebrates (lizard, duck, &c.), may be 

 of a similar nature. 



The indefinite anterior termination of the notochord beneath 

 the hind-brain, just behind the pituitary body, audits segmental 

 swellings in this region, may be compared to the gradual dis- 

 appearance of the spinal artery in the same region just behind 

 the merochord, and to the segmental swellings of the artery 

 between the successive neuromeres. 



The '' godets " of Moreau found in Amphioxus may be 

 remnants of arterial branches ; and the origin of the chorda 

 cells from the sheath may be compared to the origin of blood- 

 corpuscles from the wall of the spinal artery. 



The fact that the notochord does not at first lie for its 

 whole length in the ectoderm may be regarded as a secondary 

 condition, all its very early phylogenetic stages being passed 

 over hurriedly in the primitive streak, or growing-point. 



VIII. The Botryoidal Cord. — Beneath the spinal artery of 

 Scorpio lies a remarkable rod-like body which I shall call the 

 botryoidal cord. It develops as a forward growth from a 

 great primitive-streak-like group of cells, in much the same 

 way the notochord of Vertebrates does. The primitive streak 

 itself is at first situated at the posterior end of the body, but 

 when the tail fold arises it lies just at the junction of the tail 

 with the posterior end of the abdomen ; the primitive streak 

 then seems to produce tissue in both directions. At first it is 



