432 F. H. Krecker, 



As the niimber of cells increases tlicy form a disorganized mass 

 in the coclom whicli may extend quite a distance toward the anterior 

 end (Fig. 20). In this position their activity does not cease. They 

 continue to divido, as the various stages of division indicate, so that 

 tJieir niimber is increased both by recruits froni the ectoderm and by 

 the division of those abeady in the mass. After these enlarged ecto- 

 derm cells have oiice rcached the coelom and collected in a group it 

 is impossible to distinguish them from the neoblasts. They are similar 

 in the cliaracter of the nucleus, cell body and staining reactions and 

 so far as it is possible to judge they are neoblasts. 



This remarkable change in the cliaracter of the ectoderm cells 

 and the factors which may bring it to pass are at least of great intercst 

 and it will be worth while to coiisider the subject more closely. It is 

 possible that there is a predetermined area in the ectoderm witliin which 

 this enlargement of cells occurs v/hen the worm is cut in two. The 

 fact that the enlargement always takes place on the ventral side and 

 not far from, usually on both sides of, the nerve cord lends some support 

 to this assumption. It was thought that by keeping individiials in an 

 inverted position several points in question might be settled. If the 

 dorsal side is made to lie lowermost will the cliaracter of the ectoderm 

 change on this side? Do the neoblasts lie on the ventral side of the 

 body because kept there by the force of gravity and if they move to 

 the dorsal side will they be foiind around an area of metamorphosed 

 ectoderm? In an attempt to determine these problems the following 

 experiment was carried out. Several worms were cut in two and the 

 head pieces, from some of which a bit of the intestine liad been removed, 

 were placed between two ordinary glass slides. Pieces of cover glass 

 supported the slides sufficiently to prevent them from crushing the 

 Worms without, hf)wever, allowing the worms to turn over. Only one 

 worm was placed between eacli set of slides. The sj)ace about the worin 

 was filled with water and the slides were held together by a rubber 

 band. Then the slides were inverted so that the ventral side of the 

 worm was uppermost and they were kept in a damp chamber to prevent 

 the evaporation of the water. The worms were kept under these con- 

 ditions for ten days or two weeks and then sectioned. In none of the 

 individuals had the neoblasts moved to what is normally the dorsal 

 side and in none had the septa begun to form or the ectoderm to change 

 its character on this lower side. The neoblasts were gathered about 

 the end of the nerve on the ventral side, in this case the uppermost 

 side, just as they would have been had the worm not been inverted. 



