Ill] OF REGENERATION 275 



In certain minute animals, such as the Infusoria, in which the 

 capacity for regeneration is so great that the entire animal may- 

 be restored from a mere fragment, it becomes of great interest to 

 discover whether there be some definite size at which the fragment 

 ceases to display this power. This question has been studied by 

 Lillie*, who found that in Stentor, while still smaller fragments were 

 capable of surviving for days, the smallest portions capable of 

 regeneration were of a size equal to a sphere of about 80 /x in 

 diameter, that is to say of a volume equal to about one twenty- 

 seventh of the average entire animal. He arrives at the remarkable 

 conclusion that for this, and for all other species of animals, there 

 is a "minimal organisation mass," that is to say a "minimal mass 

 of definite size consisting of nucleus and cytoplasm within which 

 the organisation of the species can just find its latent expression." 

 And in like manner, Boverif has shewn that the fragment of a sea- 

 urchin's egg capable of growing up into a new embryo, and so 

 discharging the complete functions of an entire and uninjured ovum, 

 reaches its limit at about one-twentieth of the original egg — other 

 writers having found a Hmit at about one-fourth. These magnitudes, 

 small as they are, represent objects easily visible under a low power 

 of the microscope, and so stand in a very different category to the 

 minimal magnitudes in which fife itself can be manifested, and 

 which we have discussed in another chapter. 



The Bermuda "hfe-plant" (Bryophyllum calycinum) has so 

 remarkable a power of regeneration that a single leaf, kept damp, 

 sprouts into fresh leaves and rootlets which only need nourishment 

 to grow into a new plant. If a stem bearing two opposite leaves 

 be split asunder, the two co-equal sister-leaves will produce (as we 

 might indeed expect) equal masses of shoots in equal times, whether 

 these shoots be many or fe^^; and, if one leaf of the pair have part 

 cut off it and the other be left intact, the amount of new growth 



* F. R. Lillie, The smallest parts of Stentor capable of regeneration, Journ. 

 Morphology, xii, p. 239, 1897. 



t -Boveri, Entwicklungsfahigkeit kernloser Seeigeleier, etc.. Arch. /. Entw. Mech. 

 u, 1895. See also Morgan, Studies of the partial larvae of Sphaerechinus, ibid. 

 1895; J. Loeb, On the limits of divisibility of living matter, Biol. Lectures, 1894; 

 Pfluger's Archiv, lix, 1894, etc. Bonnet studied the same problem a hundred 

 and seventy years ago, and found that the smallest part of the worm Lumbriculus 

 capable of regenerating was 1^ lines (3-4 mm.) long. For other references and 

 discussion see H. Przibram, Form und Formel, 1922, ch. v. 



