76 ELIOT K. CLARK 



Nach dicser Abbildung Dareste's und einigcn von mir zufallig auf- 

 gefiindenen, weit ausgebildeten Fallen treten in dieseni Capillarnetz 

 schon einige den normalen grosseren Gefassen entsprechende Richti- 

 gungen deutlich hervor, wie ich sehe, die entsprechende Erweiterung 

 derselben und die Verdickung ihrer Wandung f ehlt ; der Sinus terminalis 

 ist jedoeh ausgebildet und beweist so allein schon die vererbte lo- 

 calisierte Anlage eines typischen Gef asses. 



Embryos without circulation were produced by J. Loeb ('93) 

 who found that, by growing embryos of fundulus, a salt water 

 minnow, in the proper concentration of potassium chloride, the 

 beat of the heart could be entirely eliminated, or so diminished 

 that all circulation of the blood was absent. The development 

 of the embryo, however, continued for several days — about half 

 the normal hatching time. In such embryos Loeb found an ex- 

 tensive development of blood-vessels which, except for irregu- 

 "larities in caliber, resembled in distribution the vessels in normal 

 embryos. He concluded that: 



Die mechanischen Ursachen fiir das Wachstum der Gefasswande 

 sind deshalb nicht im Gefasslumen zu sucheii, sondern in alien oder 

 einzelnen Zellen der Gefasswande und die Abgabe von Aesten ist 

 bestimmt durch innere Ursachen in den Zellen der Gefasswande oder 

 durch Reizursachen, die von der Umgebung ausgehend, diese Zellen 

 treffen, ahnlich wie im Falle der Stolonenbildung von Hydroidpolypen. 



Patterson ('09, pp. 87-88) studied the area vasculosa of chick 

 embryos in which the development of the embryo proper had 

 been prevented by operation upon the unincubated blastoderm. 

 He describes the finding of vessels which radiate toward the re- 

 mains of the embryo, and which he interprets as omphalomesen- 

 teric arteries. 



Knower ('07) studied the development of frog larvae from 

 which the heart anlage had been removed before pulsation had 

 started. In a brief summary he states that — ''the aorta, the 

 large veins and the segmental vessels are laid down." "Both 

 arteries and veins are very abnormal and have a few well-defined 

 branches. All vessels become much distended and follow very 

 irregular courses." He found no vessels in the fin expansions of 

 the tail. 



