28 



SCIENCE. 



[N. S. Vol. XIV. No. 340. 



SOCIETIES AND ACADEMIES. 



ZOOLOGICAL CLUB, UNIVERSITY OF CHICAGO, 

 WINTER QUARTER, 1901. 



II. 



At the meeting of February 6 the pro- 

 gram consisted of a paper by Mr. C. M. Child, 

 entitled ' Regulation in Stenostomum. ' 



This paper dealt chiefly with some of the 

 phenomena of regulation following the cutting 

 of an asexual chain of Stenostomum-zooxds at 

 various points. Some of the more important 

 points are as follows : 



The changes which occur after cutting a chain 

 of Stenostomum- zoo'ids differ greatly according 

 to the position of the cut with respect to the 

 zones of fission and according to the stage of 

 development of the latter. 



Pieces above a certain relative size, cut 

 within the limits of a single zooid, regenerate 

 the anterior and posterior ends without the 

 formation of a distinct bud of new tissue, al- 

 though prolifei-ation occurs at the cut surfaces. 

 A very rapid change of form occurs, the piece 

 becoming longer and more slender and acquir- 

 ing the ' normal ' form of a Stenostomum indi- 

 vidual. The time required for the completion 

 of the regulation varies with the temperature, 

 but is in all cases very short. At a tempera- 

 ture of 75° F. it is only three or four days. 



If the piece consists of parts of two or more 

 zooids, i. e., if it contains one or more zones of 

 fission, the processes of regulation are more 

 complex. In pieces consisting of the posterior 

 portion of one zooid and the anterior portion of 

 the succeeding zooid the changes depend upon 

 the stage of development of the organs about 

 the zone of fission. If the zone of fission be at 

 a very early stage it may disappear entirely, 

 the whole piece becoming a single individual 

 with head and tail at the two ends. In this 

 case the part which was destined to become the 

 posterior half of an individual becomes, in con- 

 sequence of its separation from the chain, the 

 anterior half, while the portion behind the zone 

 of fission, which was destined to become the 

 anterior half of an individual, now becomes the 

 posterior half. 



If the zone of fission is older, i. e., if the new 

 brain behind it is well established, all that por- 



tion of the piece which lies in front of the zones 

 of fission is absoi'bed by the part posterior to it, 

 i. e. , the part which possesses the brain. This 

 occurs even though the anterior piece is much 

 the larger. As the anterior piece is absorbed 

 it is reduced in size, and the zone of fission and 

 the brain appear to migrate in the anterior di- 

 rection until finally they reach the anterior 

 end of the whole piece, i. e. , until the anterior 

 part is completely absorbed. In a recent paper 

 (Proc. Cal. Acad, of Sciences, Ser. III., Zoology, 

 Vol. I., No. 6, 1901) Ritter and Congdon have 

 asserted that the brain actually does migrate in 

 pieces of this kind. This seems to be an error 

 of interpretation. Continuous observation of 

 the pieces shows that the facts are as stated 

 above. Indeed, the migration of the intestine 

 out of the anterior piece can be observed. 



If the zone of fission has reached a late stage 

 of development, so that the brain of the pos- 

 terior zooid is well formed and the pieces are 

 more nearly ready to separate, little or no ab- 

 sorption of the anterior piece occurs and the 

 two pieces separate as they would under normal 

 conditions, the anterior pieces developing a 

 new head and the posterior piece a new tail at 

 the respective cut surfaces. 



The absorption, when it occurs, is always in 

 the posterior dii-ection, i. e., the part deprived 

 of a brain is absorbed by the part which still 

 retains the brain. The actual disappearance of 

 the zone of fission occurs only in the early 

 stage when the brain posterior to it is not de- 

 veloped or is at a very early stage of develop- 

 ment. In general the results depend upon the 

 presence or absence, or the relative develop- 

 ment, of the brains in the parts of zooids which 

 make up the pieces. 



In sexual individuals of Stenostomum asexual 

 multiplication ceases, though the single individ- 

 ual may attain a length as great as a chain of 

 eight or more sexual zooids. The power of 

 regeneration in sexual individuals is not as 

 great as in the asexual chains. The energy of 

 the body appears to be directed in large part 

 toward the elaboration of the sexual products, 

 the consequence of this condition being the 

 cessation of asexual multiplication and the re- 

 duction of the power of regeneration. 



The session of the Club held on February 



