366 EMBKYOLOGY OF THE LOWER VERTEBRATES CH. 



modification of (1) brought about by a hurrying on of the develop- 

 ment of the corpuscles. 



(3) In still other cases the cells of the mesenchyme reticulurn in 

 certain localities e.g. in the spaces between the tubules of the 

 pronephros draw in their processes, round themselves off and are 

 carried away in the blood stream as primitive corpuscles. 



This last mode of origin may account for the fact that the 



enc. 



enc 



rnc. 



D. 



Fi'.. 176. Portions of transverse sections through Khisinobram-.h rmliryos illustrating 

 the origin of the heart. 



A, Tor)w.lu, stage with one #ill cleft; B, 7'<>;/'-'/u. sia^' 1 \\ith two xill clefts; e, 1'riatini-i^ 

 with twenty-fhi: s'-iin-nts : l>. Pristiurvi, sl:i-- with forty .sr.-nn-nts. (After li-mcs l.y Kuck.-it 

 (1S88) and Moliier (I'.'OO).) /.//(. dorsal iiu-socardiiini ; enc, finlDcardium : '//(/, ciKlodt-i m of loi.-nt : 

 : HI ; N, notochnrd ; /, pci icai iliac cavil \ ; 8.0, spinal cord ; >-;>/f, 



corpuscles have been observed to make their appearance suddenly in 



numbers in the circulating blood. The sudden setting Inv 



of large numbers of corpuscles is -possibly due to an epidemic d 



i ihr nicH'iirhvnie cells, as it is well kno\vn thai the onset 



of tin; inilotir process I'l v. pimtl y iinlucus a retraction of tin- processes 



of the cell hody and its a^iimpt iu of an approximately spherical 



sha| 



1 1 i- not propo.-ed i. i race out in this \ohiine 1 he further develop- 

 ment of the hlood c,,i-puseles ho\\ I he originally similar indilfereiil 



