1894. ''PREFORMATION OR NEW FORMATION:' 187 



somatic and sexual cells, once it has arisen, is inviolable, then we are led 



to strange conclusions. For instance, in two forms so nearly allied 



as Volvox glohntor and Pandorina morum, we should have to assume 



that Pandorina had no soma, for all its cells can reproduce : while in 



Volvox, where certain cells are specialised as sexual cells, there is a 



soma. 



III. — Reproduction and Regeneration. 



A multitude of cases show that very many cells and tissues contain 

 the possibility of reproduction. Thus, a plant like Funaria hygro- 

 metrica may be chopped in tiny pieces, and each piece, placed in damp 

 earth, will reproduce the whole plant. Similar occurrences are familiar 

 in cases like the willow, the begonia, or in many coelenterates, worms, 

 and tunicates. It is making a large drain on the imagination to 

 suppose that in so many widely-scattered cases a condition diame- 

 trically opposed to what Weismann regards as the normal condition 

 of complete separation between soma and germ-plasma has arisen 

 under special conditions. 



I V . — Hetevomorphosis . 



Loeb uses this term to denote the power of organisms, under the 

 stimulus of outer conditions, to produce organs on parts of the 

 organism where they do not occur normally, or the power to replace 

 lost parts by parts unsimilar to them. Regeneration is the repro- 

 duction of like parts. Heteromorphosis is the reproduction of unlike 

 parts. 



If one cuts off part of the stem of almost any plant, on placing 

 the stem in suitable soil, roots will grow out, although roots are not 

 natural to that part of the stem. The prothallus of ferns produces 

 the male and female organs on the lower side turned away from the 

 light. If a prothallus be darkened on the upper surface, and illumined 

 by reflected light on the lower surface, then the antheridia and 

 archegonia will be produced on the upper surface. Galls are pro- 

 duced under the stimulus of the insect almost anywhere on the 

 surface of a plant. Yet in most cases these galls, in a sense 

 grown at random on the surface of a plant, when placed in damp 

 earth will give rise to a young plant. In the hydroid Tuhnlaria 

 mesemhryanthemnm, when the polyp-heads are cut off, new heads 

 arise. But if both head and root be cut off, and the upper end be 

 inserted in the mud, then from the original upper end not head- 

 polyps but root filaments will arise, while from the original lower 

 end not root filaments but head-polyps will grow. In Ciona 

 intestinalis round a slit cut into the body-wall a tubular process grew 

 out, forming a new mouth, while round the base of this, a series of 

 eye-spots, corresponding to the eye-spots round the real mouth, 

 appeared. In all these cases, it is plain that there were present in 

 parts affected the determinants, to use Weismann's term, not only 

 of the normal parts, but also of parts which, under normal conditions, 

 would never have appeared there ; and these new parts growing in 



