ESTIVATION OF BOTRYLLOIDES GASCOI DELLA VALLE. 159 



region of greatest growth had left the place where the first system was formed and 

 had migrated back over the opaque part of the colony, apparently causing an entirely 

 new lot of buds, which had been lying dormant hitherto, to develop. By August 12 

 two incipient systems had been formed in this region. On August 15 (Fig. 3) one of 

 these had entirely disappeared and the other had formed the second well-defined 

 system of the rejuvenating colony. But the point to be noted here is that there was 

 no definite genetic relation between the first and second systems. They may have 

 belonged to the same generation of buds, but it is more likely that the second was 

 produced from an earlier generation that was lying dormant until stimulated by the 

 abundant food furnished by the migration of the region of greatest growth. 



The last generation will be called Generation x. It began to degenerate on 

 August 16, one day after the formation of the second system; but the various zooids 

 degenerated at very different rates. One in particular (Figs. 3-9, 3) was so slow in 

 degenerating that it still had its siphons open on August 19, when the next generation 

 (x + 1) was nearly adult. On the next day the zooids of Generation x + 1 opened 

 their siphons and formed the third system, but it is doubtful whether zooid 3 was a 

 member of this system or had degenerated entirely.* From August 20 on, the budding 

 progressed normally until about September 10, when the opaque part of the colony 

 had died and the transparent growing part had entirely regained its former vigor. 



It seems, then, that the facts given in this section fully bear out the statement 

 made at the beginning, that, in the rejuvenating colony, the usual reproductive coor- 

 dination is lost. I think that the cause of this difference between the normal and 

 rejuvenating colony is to be sought in the difference of the circulation maintained in 

 the two cases. In the normal colony the hearts of the zooids and buds everywhere 

 keep up a vigorous circulation, and this is still further assisted by the contractions 

 of the ampullae, which are also distributed throughout the colony, but are more numer- 

 ous about its edges. Hence a vigorous circulation is kept up in all parts of the colony 

 and all the food is evenly distributed. In the rejuvenating colony, however, the 

 food-supply did not seem to be large enough to maintain all parts of the colony in a 

 vigorous condition. For this reason, or possibly for some other, only a small part of 

 the colony could be maintained in a vigorous condition. This part I called the grow- 

 ing edge, as it was the onby part of the colony that was occupying new ground. On 

 page 154 it was indicated that the growing edge was also the region where the ampullae 

 contracted most vigorously and maintained the best circulation. As the vigor of 

 the circulation varied in different parts of the colony it follows that the food must 



* On August 19, in that part of the colony where the incipient system disappeared August 15, a single small 

 bud appeared, but had almost entirely degenerated on th e next day. It probably belonged to Generation x + l.[ 



