BLOOD VESSELS OF LUMBRICUS. /5 



worm confirm the above results ? (2) What is there in the 

 structure of the blood vessels to determine and control the 

 course of the blood ? 



The first question has been answered by a series of regenera- 

 tion experiments carried out upon large and small specimens of 

 Lwnbricits. Operations removing from eleven to twenty somites 

 from the anterior end were performed upon 171 worms. These 

 were examined alive from time to time and eventually 20 were 

 hardened for sectioning. The time that the worms were allowed 

 to live varied from ten days to three and a half months. In a 

 few worms regeneration progressed well, but the majority died 

 after a few days or weeks. A detailed report upon these experi- 

 ments would not be profitable for our present object. Although 

 there were very great variations in the condition of the blood 

 vessels, the following may be said to be true in greater or less 

 degree of all the worms studied alive or sectioned. The vessels 

 in the anterior one fourth to one half of the worm were greatly 

 crowded and distended with blood. The anterior portion of the 

 worm was usually a bright red to the naked eye and under a 

 lens many small vessels not usually visible were distinctly seen. 

 Sections showed that all the vessels were more or less crowded 

 with blood, while the dorsal, subneural, and the vascular plexus 

 of the intestinal wall showed the greatest distension. The ven- 

 tral vessel was seldom stretched much beyond its normal size, 

 while the subneural was often as great in diameter as the ventral. 

 Occasionally the subneural was much larger than the ventral and 

 sometimes its cross-section was equal to that of the nerve cord. 

 In several cases the vascular layer of the intestine was very 

 greatly crowded and, considering its great capacity in normal 

 conditions, it is probable that it always held the greatest accu- 

 mulation of blood. The posterior portion was very poor in blood 

 in all worms. 



These conditions are readily explained in accordance with the 

 scheme of circulation above summarized. The fulness of the 

 dorsal, intestinal and subneural vessels is due to the pressure 

 from the dorsal which is deprived of the normal outlet for the 

 blood carried by it, and forces the blood downward in the dorso- 

 intestinals and parietals contrary to its usual course. The small 



