July 5, 1901.] 



SCIENCE. 



29 



20 was devoted to an accouat by Mr..E. H. 

 Harper of 'Regeneration in Nais lacustris.^ 

 The paper comprised the results of experiments 

 on both sexual and asexual individuals of this 

 species. The following is a brief abstract : 



In the asexual forms where from one to 

 five anterior segments are removed the same 

 number is regenerated as was cut off. In this 

 region in the sexual forms the head segment 

 alone is regenerated, or frequently the surface 

 heals over without regenerating. 



When more than five segments are removed 

 in the asexual forms a pharyngeal region of 

 five segments is regenerated. In the sexual 

 animals the process is much slower and in an 

 advanced sexual stage a dwarfed region of five 

 very short segments is produced. The clitellum 

 and sexual organs may be regenerated. This 

 has been seen to occur after a considerable 

 time. 



So far as could be determined mutilation 

 never causes the disappearance of the sexual 

 organs, but the formation of a regenerating 

 region will under certain conditions inhibit the 

 process of asexual multiplication and cause the 

 disappearance of the zone of fission. This 

 effect may be produced by a cut anterior to the 

 zone of fission, less often by a cut posterior to 

 it, and occurs only when the zone is embryonic. 

 The zone is also more likely to disappear if the 

 cut is near to it. The band of transparent 

 embryonic tissue redifferentiates and the energy 

 of growth is transferred to the regenerating 

 region. 



In the asexual individuals the power of 

 regeneration is less in the anterior specialized^ 

 region and also in the posterior budding region 

 than in the middle of the body. Short pos- 

 terior pieces may live a considerable time, but 

 do not regenerate. Anterior pieces of eight or 

 nine segments may survive a short time with- 

 out regenerating, but pieces of the same length 

 from the middle of the body regenerate 

 freely. 



Internal conditions favorable to prolifer- 

 ation, such as the exposure of cut surfaces of 

 intestine and blood vessels, are present in 

 nearly all possible experiments. But if a cor- 

 ner of the head segment be removed, including 

 the prostomium, without injuring the pharynx, 



the ectoderm will close over the surface and 

 regeneration will not take place. In the sexual 

 forma failure to regenerate may occur when the 

 pharynx is cut through. Here the tendency 

 to proliferate is slight and it may be that the 

 epithelium differentiates completely over the 

 cut surface before any appreciable amount of 

 regeneration has occurred. And it is probable 

 that after the epithelium is formed there is no 

 further tendency to regenei'ate. 



Growth takes place at right angles to a cut 

 surface ; and if the cut is oblique the bud will 

 grow out at an angle to the axis of the bod5\ 

 Straightening is effected after the j)enetration 

 of the lumen of the intestine into the region 

 under the influence of its peristaltic mo- 

 tions. 



Many of the internal iihenomena of regen- 

 eration may be observed in the living animal 

 on account of the transparency of the body 

 wall. Migration of pigmented cells from the 

 intestine toward a regenerating region can be 

 seen. If a corner of the head segment be cut 

 off, including one eye, the pigmented portion of 

 the other eye is usually fragmented and pig- 

 ment migrates in various directions. 



It has been stated that the regenerative 

 power of these animals varies with the season 

 of the year, being less in autumn and winter. 

 No evidence of this has been observed, but the 

 evidence points rather, as we have seen, to an 

 inverse correlation between regenerative power 

 and sexual activity. Budding, i. «., asexual, 

 individuals regenerate freely and completely in 

 December. The sexual forms ai-e found from 

 October to December. 



The program for the meeting of March 6 

 consisted of two papers, ' The Excretory Sys- 

 tem of the Bryozoa,' by Miss A. W. Wilcox, 

 and ' Montgomery on the Spermatogenesis of 

 Peripatojjsis,^ bj?^ Mr, E. R. Downing. 



Miss Wilcox reviewed the literature upon 

 the excretory organs of the Bryozoa and gave 

 the results of some work of her own on the 

 Phylactolaemata. Her paper will appear in full 

 elsewhere. 



Mr. Downing' s paper consisted of a review 

 and discussion of Montgomery's recent study 

 of the spermatogenesis of Pei-ipatopsis. 



C. M. Child. 



