UN I ATE LATER OR ME*ENCHYME. 551 



'"in) the mod > 'lood-corpuscles sti ie to 



lie in groups ,,,, tin- ualU o| the tube*. 



ouiij described WooMiUmd* (fig. 11 h. which mise the red- 



be>prinkl-d ftppS*nUM6 of the VMOOlM MM, //< mtraciiotu oj 

 tin* Jti-'ii't. liy \\hich the blood is set in motion, are at first slow and 

 then become more and more rapid. On the average, according to 

 PBIYER, the strokes then amount bo LBO- lfl 



tin- Erequenoy of pulsfttioofl is largely depen<i external 



intluenecs; it increases with the elevation ..f the temperature of 

 incubation and diminishes at .-very depression of it, as well as when 

 the egg i- t.) rued l'"r Mudy. At tli time when the heart begin* to 

 1'iilsuto. no muscle-librill:- have been demonstrat'-d in the myocar- 

 dium ; from thi^ roult- tli-- int.-i .-( n._ purely j.roto- 

 plaMiiic. Mill iindiU'civntiatrd o-ll> an- in a OOU rong 

 rhythmical contractions. 



At the end of th- thinl or t'onrth .i 



in tho Chick is at its hirh >t development ; it has undergone some 

 slight chant's. \\'c lind instead of a single va .etwork a 



double one, an arterial ami a v-n'u-. The arterial network, which 



he Mooil t'l-Din the \itrlline u s deeper, nearer \' 



yulk. while the venous spreads it>elt' out above t)i- former and i* 

 adjacent to the visceral middle layer. The cii : blood is 



diMii.giii-hed by the abundance of its blood-corpuscles, the blood- 

 island- ha\ iiii: entirely .r-appr;: 



Til- is twofold. Fit>t it serves 



io\i<le the bl.dd with t'xygrn, op|H.i ;uiring \\hich 



is afforded by the whole vascular network bring >pread out 

 at the surface of the egg. Secondly it serves to bring nun 



MlhMailce^ to the eml : tS below | MaSt 



are disassociated, liquefied, and taken up into the blood-vessels, by 



which they are carrir. 1 to t he embryo, where they serve as nun-. 

 for the rapidly dividing cells, 'i the embryonic body 



increases in size at the expense of 

 sac, which becomes liquefied and absorbed. 



Thr >\ -tem of vitclline blood-vessels in Mammals agrees in general 

 with that of the Chirk nguished from the latt ; 



some unimportant points, which do not need to be discussed. I 



. thi> (jtirstion eeitainly arises What si^: D has a 



vitelline circulation in Mamm.iK i lig. 134 d* o egg is 



furnished with only a small amount of yolk-material I 



Two things are ; <* kept in mind : lirst. B eggs of 



