330 RANDOLPH. [Vol. VII. 



tion for regeneration. The reaction of the organism, however, is 

 not rapid ; the blood-vessels close less quickly or less completely 

 than in Lumbriculus, causing coagulation in the growing end 

 and giving to the whole worm a pale appearance. 



In Lumbriculus this process is accomplished quickly, and 

 preparations made twenty-four hours after the section of the 

 worm have an almost diagrammatic clearness. It is possible that 

 the rapidity of the growth in Lumbriculus may be the direct 

 result of the prevention of the waste from the broken ends of 

 the blood-vessels. The great size of the neoblasts is doubtless 

 in direct relation to the rapid regeneration in this form. 



The development of the budding zones in Nais elingiiis is 

 characterized by remarkable rapidity. The great increase of 

 tissue becomes quickly an accomplished fact, instead of exhibit- 

 ing a progressive development such as takes place in ordinary 

 growth. It is probably of great advantage to the worm to have 

 the period during which the middle region of its body is occu- 

 pied by an inert mass as much shortened as is possible. This 

 probably causes simultaneous development and, together with 

 the rapid accumulation of new tissue under pressure at both 

 ends of the growing zone, tends to obliterate the steps by which 

 the process is brought about. 



In Chaetogaster the development is even more rapid and more 

 compressed than in Nais. 



The formation of budding zones is begun, as is well known, 

 by the multiplication of peritoneal cells, which correspond to 

 the neoblasts of Lumbriculus. 



The largest neoblasts of the series are those of Lumbriculus, 

 and those of Tubifex are second in size. I have not seen any 

 evidence of division of the neoblasts in these two forms until 

 after the division of the worm. It is probable that there is a 

 tendency in the direction of storing up as much material as 

 possible in each neoblast in preparation for the great and sud- 

 den demand for regeneration. In those forms in which agamic 

 reproduction has become established, there is a preliminary 

 or introductory stage of multiplication of undifferentiated cells, 

 which therefore do not need to attain to so great a size. With 

 the increase of the tendency to accumulation beyond the size 

 limit of the neoblast, the conditions for cell division would exist, 

 and with cell division the process of budding is essentially 

 begun. 



