116 SECTIONAL ADDRESSES. : 
functioning as a part of the whole, and that each cell has in addition the 
opposite faculty of dedifferentiation—of becoming young and resistant at 
the same time. When this rejuvenated cell develops either singly or in 
company with other dedifferentiated cells, the resultant in either case 
exhibits a new metabolism and a new orientation, giving rise to an organ- 
ism with typical arrangements of dominance and subservience of parts, 
such as characterise all normal animals. 
The morphology of fixed colonial animals such as corals acquires fresh 
interest when considered in the light of this principle. Wood-Jones (8), 
as Child has pointed out, has found from a study of living Madrepora 
under natural conditions, that there is an apical radially symmetrical zooid 
at the top of the stem which give rise by budding to bilaterally symmetrical 
lateral zooids. These, however, do not bud off others so long as the apical 
zooid is present and active, until by growth of the whole ‘ shoot’ they 
become separated by a certain distance from the dominant apex. When 
that occurs, one of them becomes transformed into a radial member, puts 
out lateral zooids and becomes a new apex. If the apical shoot and stem 
are removed, several branches may arise by transformation of bilateral 
into radial reproducing zooids. The whole process so strikingly recalls the 
fundamental relations of dominance and isolation leading to organic repro- 
duction in animals and also in plants that Child does not doubt the general 
applicability of the principle to organisms in general. 
(C) Independence of the Apical Region. 
One of the most striking pieces of evidence on the subject of regeneration 
is the work of Ivanov on certain sea-worms, Spionids and Serpulids. 
Unfortunately, the greater part of the work (1912) is in an inaccessible 
Russian dissertation (9), but the first part of it appeared in 1908 as a 
continuation of his earlier researches on Lumbriculus, a fresh-water worm. 
In order to make the results clear, reference must be made to Ivanov’s 
division of the Annelid body. By reason of certain peculiarities of the 
mesoderm of the anterior segments, he accounts as cephalic, or, as he 
later calls them, ‘ larval’ segments, not only the prostomium and peristo- 
mium of zoological nomenclature (i.e. the apical and sub-apical segments), 
but those which follow, so long as they possess certain mesodermal 
characteristics. The rest of the body he calls ‘ post-larval.’. This post- 
larval body is specialised in Serpulids into a thoracic and an abdominal 
portion. If now ‘the head’ or three larval segments of Spirographis be 
removed, the process of regeneration is no simple or direct operation, but 
resembles, to a remarkable degree, the embryonic development of these 
segments ; whilst the regeneration of the body-segments proceeds in a 
different way, but also along the lines of the embryonic development of 
that region. What, however, chiefly concerns my argument is the establish- 
ment of a new head, not by morphollaxis (dedifferentiation followed 
by reconstruction on a new type), but by the appearance of an apical plate 
typical of the trochosphere stage, of pre-oral antennae (which have dis- 
appeared from the Serpulid trochosphere), and of the cerebral ganglia by 
thickenings that correspond to the ciliated pre-oral bands of the trocho- 
sphere. The interior of this dedifferentiated thoracic end of the decapitated 
body is now filled by immigration of ectoderm cells that assemble in three 
—s- 
