. The elements of experimental embryology. Embryology, Experimental; Embryology. 300 FIELDS AND GRADIENTS. Fig. 142 a perisarc which acts as a handicap to all regions within it, and permits of regeneration only at the ends. In Corymorpha, however, the perisarc is absent over most of the stem-length in large specimens. As a result, multipolar forms often arise, especially from short fragments^ (fig. 142). A very striking example of the multiple production of dominant regions is seen in the sea-anemone Harenactis, When portions of the body are isolated, they roll up to produce hollow structures
. The elements of experimental embryology. Embryology, Experimental; Embryology. 300 FIELDS AND GRADIENTS. Fig. 142 a perisarc which acts as a handicap to all regions within it, and permits of regeneration only at the ends. In Corymorpha, however, the perisarc is absent over most of the stem-length in large specimens. As a result, multipolar forms often arise, especially from short fragments^ (fig. 142). A very striking example of the multiple production of dominant regions is seen in the sea-anemone Harenactis, When portions of the body are isolated, they roll up to produce hollow structures like a tyre, the original distal and proximal cut surfaces meeting and growing together. It is then found that regeneration is initiated at a number of places along the line of suture. Regeneration is found especially at places where, owing to irregularities of the cut surfaces, union has not been smooth. At each of these spots, conditions are .tta^anelf^^SS'Te;" favourable for new growth, and diagram of Harenactis to show {a and therefore the establishment of new ^) sections isolated for regeneration. , These roll in to torm hollow tubes, as apical organs ; and the various shown (centre) in section: the distal regions of new growth are isolated and proximal cut surfaces unite in a r 1 .1 1 ^1 • suture, here shown centrally. Right, from each other by other regions regeneration of apical regions (whole in which smooth union, leaving no or partial tentacle groups) from the free cut surface, has taken place.'^ suture. When the suture is irregular, ' . ^ with considerable prohteration, a As Will be seen m the next chap- number of apical regions can arise ter, these phenomena of double (above); when the union is smooth, , . 1 . . one regenerate dominates and inhibits or multiple organisations arising ^^^ development of others (below). from a single portion of tissue are (After Child, Physiological Foiinda- of great interest in the interpreta- tions of Behavior, New York, 1924
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