124 THE AMERICAN NATURALIST.  [VOL. XXXII. 
less after the second cut than after the first? Experiment showed 
that it is so; that, whereas it takes five and one-half days on the 
average for regeneration to occur after the first cut, it is effected 
under otherwise similar conditions in three days after the second. 
The repetition of the stimulus quickens the response. 
If a piece of the stem of Tubularia be cut at both ends, regeneration 
will take place at both the oral and the aboral end. If, now, in one 
case the oral end be sealed with wax so that it cannot grow and the 
aboral be left free to regenerate, will the time required for the for- 
mation of the aboral head differ in the two cases? The result showed 
that regeneration of the aboral head occurred in all cases inside of 
seven days after the cut when only one head was forming, whereas 
it took over twelve days when both heads were arising. Regenera- 
tion is slower when the formative stuff goes to two points than when 
it aggregates at only one. 
The tentacles of Tubularia surround the oral end at two levels. 
After decapitation, consequently, reparation of tentacles occurs at 
two zones, a distal and a proximal. The question arises: What 
will happen if after reparation has begun in both zones the distal 
zone is cut off? Will a head with only one zone of tentacles arise? 
Here the marvelous phenomenon of regulation was most strikingly 
shown. The normal number of zones was regained, and, indeed, by 
either one of four modes, all producing the same end result, —- the 
restoration of the perfect form of the adult. These four modes are: 
(1) by regeneration — the cut end grew out, and in this regenerated 
_ part the distal zone of tentacles arose by reparation; (2) by dissolu- 
tion —the remaining (proximal) zone of tentacles was dissolved 
and in its place the normal condition of two zones appeared ; (3) by 
replacement — the distal zone having been removed so as to leave 
the maximum space beyond the proximal zone, a new series of ten- 
tacles sometimes arose in this empty space without disturbing the 
proximal zone; (4) by division — the arising tentacles of the proxi- 
mal zone disintegrated in their middle, forming the two zones char- 
acteristic of normal development. 
Determination of Sex in Plants. — The causation of sex in the 
hemp plant, studied at various times in the past, forms the subject 
of a short communication in the Comptes Rendus of the French 
Academy for Nov. 15, 1897, by M. Molliard, who concludes from 
his experiments that the medium in which the plant grows may 
affect its sex, and that, in this case, contrary to the currently admitted 
