256 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Echinoderma. 



Hybridization Experiments with Sea-Urchins. — 0. Koehler 

 (Zeitschr. induktiv. Vereriungslehre, 1916, 15, 1-163, 177-295, 7 figs.). 

 Description of variations of the four-armed phitens larva which results 

 from crossing Strotigylocenti'ot us Uvidus 6 and Sphaerechinus gramdaris ? . 

 The characters may be mainly maternal, or mainly paternal, or inter- 

 mediate. The difference of, result depends partly on temperature, which 

 inhibits the primordia of one parent or the other. Another factor is the 

 age of the gametes, the " transmitting power " diminishing after a 

 certain degree of ripeness. The characters which find expression in 

 the larva will depend on the relative age of the two gametes at 

 fertilization. J. A. T. 



Coelentera. 



Is there a Metabolic Gradient in Tubularia ?— Mario Garcia- 

 Banus {Jourii. E'xper. Zool, 1918, 26, 265-73). According to C. M. 

 Child an excised piece of the stem of Tuhularia regenerates a new 

 hydranth at the oral end the more rapidly the nearer this end lies to 

 ihe original apex of the stem. He assumed that this regional difference 

 in the rate of regeneration is due to a difference in " metabolic rates," 

 i.e. to the existence of a metabolic gradient. But the differences iu the 

 time of regeneration observed by Child were so small that they seemed 

 to lie within the limits of error of such experiments. The author 

 repeated Child's experiments and found that the rate of regeneration of 

 the oral hydranth of an apical piece is on the average identical with the 

 rate of regeneration of the oral hydranth of the basal piece. There is 

 no evidence of the existence of level or regional differentiation of the 

 rate of regeneration in the stem of this hydroid, and no basis, therefore, 

 on this line for the theory of axial gradient in this species. J. A. T. 



Asexual Multiplication and Regeneration in Sagartia Incise. — 

 Donald Walton Davis {Journ. Exper. Zool, 1919, 28, 161-263, 

 10 pL). This anemone is typically Hexactinian in form and structure, 

 except for the wide variation in the number of siphonoglyphs (1 to 5) 

 and complete mesenteries (5 to 12). Asexual reproduction occurs by a 

 process of aboral-oral fission with subsequent regeneration, which is 

 described in detail. The resulting pieces may possess one or more 

 siphonoglyphs and associated pairs of directive mesenteries, or they may 

 lack these until regeneration has occurred. Another division may 

 occur before regeneration is complete. The plane of fission is strictly 

 vertical, rarely cutting a mesentery. There is no tendency to strict 

 equality of the products of a division. Division tends to occur in endo- 

 eoels rather than exocoels, in complete endocoels rather than in 

 incomplete endocoels, and in non-directive rather than in directive 

 complete endocoels. Regeneration processes begin with the rolling iu 

 and fusion of the torn edges of the body- wall. In the region of fusion 

 new structures are gradually differentiated, eventually constituting a 

 large proportion of the new individual. The toi'n edges of the oeso- 

 phagus also grow together, and a new siphonoglyph is always differentiated 



