10 VASCULOGENESIS IN THE CAT 



3. That the sprouts are regressive and that here, as in other 

 tissues (bone, striated muscle), progressive and retrogressive proc- 

 esses co-exist. 



4. That the 'sprouts' are the last stages in the annexation of 

 vasoformative cells which have built themselves into cords, 

 joined the lymphatics and are now estabUshing their luinen. 

 Only in this last stage would they be accessible to injection. 

 This interpretation is suggestd by Bartels ('09) and is of consider- 

 able import. Referring to certain unicellular sprouts of MacCal- 

 lum, he says: 



Gerade, dass es einzelne Zellen sind, welche die Strange bilden, 

 scheint mir eher fiir den Modus der Aufreihung dieser Zellen durch den 

 zentralwarts gerichteten Saftstrom als fur eine zentrifugal gerichtete 

 Sprossung zu sprechen. Doch will ich darauf, als auf eine nach dem 

 bisher Vorliegeiide'n nicht sicher zu entscheidende Sache, ebendsowenig 

 eingehen, wie auf die Beurteilung des Verhaltens der benachbarten 

 Gewebsbestandteile zu den Gefassen. Beides scheint mir weiterer ein- 

 gehender Untersuchungen zu bedtirfen.' 



None of these observations, important as are the data they have 

 collected, have given us the means of interpretation, once the 

 increment of vessels is conceived as a minute process which must 

 be treated in terms of cells and cell modifications. For this it 

 is necessary to work in confined areas of well understood topog- 

 raphy and with a minutely graded and continuous series of em- 

 bryos. If cords of single or double rows of cells are to be studied 

 developmentally, we must at least give ourselves the chance 

 of seeing cell add itself to cell, or the sprout ad\^ance from the uni- 

 cellular to the multicellular condition, and not work at wide in- 

 tervals of time or with material from ^-arious regions where only 

 gross comparisons are possible and minute processes may 

 altogether escape us. 



From the standpoint of possible retrogression, the work of 

 Spuler** and of Fuchs" is interesting and theii- aloofness from this 

 particular problem gi\'es their testunonj' additional importance. 



Journ. of Anat., vol. Vi, i)|). 193-220. Miller, A. M., 1913, Amcr. Journ. of Anat., 

 vol. 15, pp. 131-163. Allen, W. F., 1913, Quart. Journ. Mier. Sci., vol. 59, pp. 

 309-360. 



' Loc. cit., p. 45. « 1892, Arch. f. rnikr. Anat., Bil. 40, p. .530. 



» 1903, Anat. Hefte. Band. 22, p. 97. 



