542 THE REPRODUCTIVE FUNCTIONS. 



of that class of animals best admit of our following 

 this interesting series of changes,) the first opaque 

 object discoverable by the eye is a small dark line, 

 called the primitive trace, formed on the surface of 

 the outermost pellicle. Two ridges then arise, one 

 on each side of this dark line ;* and by the union 

 of their edges, they soon form a canal, containing 

 a deposit of semi-fluid matter, which, on acquiring 

 greater consistence and opacity, discloses two slen- 

 der and delicate threads, placed side by side, and 

 parallel to one another, but separated by a certain 

 space. These are the rudiments of the spinal 

 cord, or the central organ of nervous power, on the 

 endowments of which the whole character of the 

 being to be formed depends. We may next discern 

 a number of parallel equidistant dots, arranged in 

 two rows, one on the outer side of each of the 

 filaments already noticed : these are the rudiments 

 of the vertebrae, parts which will afterwards be 

 wanted for giving protection to the spinal marrow, 



principles above mentioned, with regard to which diastase is totally 

 inert. The quantity of saccharine product resulting from the action 

 of diastase on starch, is sixty times greater than that from the action 

 of sulphuric acid on the same substance in an equal time. Diastase 

 does not exist in the seeds of oats, barley, wheat, &c. previously to 

 the period of their germination ; it must, therefore, be formed 

 during that process. This substance has also been met with 

 surrounding the insertion of the buds of the potatoe, and of the 

 Ailanthus glandulosa, and in the vicinity of masses of fecula, 

 which are laid up as a store of nutriment to be used for the develope- 

 ment of the bud, after being dissolved and modified by the action 

 of the diastase. Ann. Sc. Nat. serie 2, Bot. x, 165. 



* The plicce prlmitivce of Pander ; the laniince dorsales of Baer. 

 See a paper on embryology by Dr. Allen Thomson, in the Edin. New 

 Phil. Journal for 1830 and 1831. 



