22 Coelenterata. 



disappeared and the yolk granules have broken up into coarse granules. In 

 a late gastrula the nutritive material lies in the ccelenteron, having passed, in 

 a practically unaltered condition, through the endoderm. The endoderm later 

 comes into contact with the ectoderm and the mesogloea is secreted between 

 them; the stomodseum is formed by inturning of the edges of the blastopore. 

 The endoderm cells become much broader, their cytoplasm less dense and 

 their nuclei less conspicuous. 



Child shows that the pieces of Harenactis attenuata, which form rings by the 

 union of oral and aboral ends about the whole circumference [ see Berieht f. 

 1909 Coel. p 47] after more or less complete removal of mesenteries and mesen- 

 terial muscles, may produce new discs with radially arranged new mesen- 

 teries and tentacles and with mouth and stomodyeum. Thus far, the usual 

 number of tentacles (24) has not been attained in any case, the largest number 

 being 16. Such discs with from 3 to 8 tentacles are frequent, but the for- 

 mation of mouth and stomodaeum has been observed only once. After the 

 discs have been formed they may be gradually elevated from the surface of 

 the rings by the development of a cylindrical column beneath the disc. Be- 

 sides the well developed discs, radially and bilaterally symmetrical and asym- 

 metrical tentacle groups may arise along the line of union on either side, or 

 the tissue of both sides may take part in the formation of a single group. The 

 new outgrowths on the rings represent a more or less close approach to new 

 individuals and involve the establishment of new polarities and symmetries. 

 The author compares the outgrowths to adventitious structures in plants. The 

 localisation of the outgrowths, as well as their polarity and symmetry, have no 

 relation to the original polarity and symmetry, but are due to local conditions. 

 The results of these experiments can be more readily interpreted in accordance 

 with the hypothesis that polarity and symmetry are essential molar locali- 

 sations or gradation of processes along an axis or axes, than with that which 

 regards them as the effect of a summation of the individual polarities and 

 symmetries of protoplasmic particles or molecules which are definitely oriented 

 with respect to an axis or axes. 



Rand found that if a distal piece is cut from a tentacle of Condylactis, or 

 other large anemone, the wall at the cut edge of the stump immediately bends 

 inwards slightly, then a broad zone of wall at the cut edge contracts until the 

 lumen is obliterated and the distended stump, now functionally closed, bears a 

 conspicuous projecting cylindrical nipple . Within two days the contracted 

 zone gradually relaxes, the nipple disappears, and the end becomes structurally 

 closed. The relatively small tentacles of Sagartia lueia behave similarly; struc- 

 tural closure is accomplished within 6 hours. A S. was kept in a solution of 

 chloretone so that muscular activity was suspended during 8 hours; neverthe- 

 less the initial inbending at a distal cut edge took place, but the zone of wall 

 which ordinarily contracts to form the nipple did not contract and a nipple was 

 not formed. A steady centripetal movement of uncontracted tissue at the cut 

 edge occurred until, in 8 hours, the cut end was structurally closed. The tem- 

 porary nipple, therefore, results from muscular contraction, but the definitive 

 closing depends upon new muscular activities, which effect a spatial readjust- 

 ment of the tissues near the cut edge. The regions of a tentacle which are 

 proximal and distal with reference to a plane of cutting, or to application of 

 a tactile stimulus, differ markedly in their reactions. The form assumed by a 

 proximal cut end is different from that of a distal cut end. In these respects 

 the tissues of the tentacles of S., like those of (7., show a distinct polarity 

 which is not explicable on the basis of their known structure. 



