214 GENERATION, 



Of the Brain and Spinal Marrow. 



It would appear, upon [examining] the most early of these parts, that 

 they were originally formed in two distinct parts, a right and a left ; at 

 least there is a transparent line which runs through their whole length, 

 dividing them to appearance into two ; but these parts are too small 

 and too tender to allow of ascertaining this as a certain fact ; and 

 indeed this division takes place in some degree in parts in the adult ; 

 for we find the cerebrum and cerebellum divided into two, as also the 

 medulla spinalis nearly divided into two, longitudinally. The union in 

 the brain of the chick seems to take place soonest about the basis of 

 the brain, making the anterior end appear as if slit into two, like a 

 pair of pincers. 



Of the Formation of the Intestines, fyc. 



The intestines, and probably the liver, spleen, kidneys 1 , &c, are the 

 latest formed ; yet the principle upon which they are formed must be 

 begun early, for the mouth is early formed, as also we may suppose the 

 anus, for the bag described as above [allantois] arises from it ; there- 

 fore there is only the intermediate canal to form, and its communication 

 with the yolk ; but as all those parts are only fitted for the second stage 

 of life, it was only necessary they should be perfected by that time. 

 The small intestines which join the yolk are drawn further out of the 

 belly as the chick grows, but before the chick hatches they are gradually 

 pulled in 2 . 



1 [The kidneys begin to be formed in the chick on the sixth day, and in the 

 tadpole as it is passing from the embryo to the larva state. But there are excretory 

 organs prior to the kidneys, called from their discoverer the ' corpora Wolffiana,' 

 consisting of hollow cseca attached to an excretory duct, and developed in birds on 

 the third day, winch secrete a yellowish urine ; so that the allantois may contain 

 urine from the first period of its existence. The corpora Wolffiana disappear in 

 birds at the time of exclusion, in Batrachia at the latter period of the larval state, 

 hi Mammalia earlier, and in Man soonest of all. See Muller, Bildungsgeschichte 

 des Grenitalien, Dusseldorf, 1830.] 



2 [The observations of Wolff on the development of the digestive organs of the 

 chick, published in 1774. are more numerous and precise than those of Hunter. Of 

 the formation of the glands Hunter says nothing. Malpighi seems to have been the 

 first who recognized the primitive form of the liver. ' Sept had terminate die' — 

 ' Jecur ipsum, subluteo mterdum suffusivm colore, quandoque cinereo, auctius et 

 solidius reddebatur, et ipsius glandulae non omnino rotundam et sphreriearn referebant 

 figuram, sed oblongiores et quasi ccecaks v.triculos, ductui hepatico appensos, repraj- 

 sentabant.' — Epist. de Formatione Pulli, p. 9. Op. Orn. fol. 1687. 



Yon Bacr and Midler perceived the first development of the liver in the chick at 

 the middle of the third day : it then appeared as two pyramidal hollow ca?ca 

 developed from the duodenum.] 



