ZOOLOGY AND BOTANY, MICROSCOPY, BTC. 149 



Echinoderma. 



Variability in Hybrid Echinoids.* — 0. Koehler reared larvae 

 from ova of Sphserechinus granulans, fertilized by spermatozoa of 

 Strongylocentrotus lividus, and observed the fluctuating variability of 

 the characters. The question is whether this is an expression of en- 

 vironmentally induced modifications, or of diverse combination of 

 Mendelian factors. His observations lead him to the conclusion that 

 an important determinant of the direction of the inheritance (from 

 similar as well as from dissimilar parents) is the relative age of the 

 gametes at the time of fertilization. 



The causes of the variability in the^ hybrids of the cross Strongylo- 

 centrotus $ and Sphserechinus 9 are exclusively internal ; they are to 

 be found in the different ages of the gametes at the moment of fertili- 

 zation, and in the occurrence of a periodic osciliation of the hereditary 

 force of the gamete with increasing age. The potency changes with 

 age. Whether the fluctuations are hereditary or not has not been 

 determined. 



Variability in Rays of Starfish.f — W. J. Crozier has collected 

 data in reference to Asterias tenuispina at Bermuda. The modal 

 number of rays is 7 ; the range in ray number is 2 to 9. The 7-ray 

 condition is uniformly the most frequent, even in widely separated 

 localities. The modal ray-number is the same for animals with sub- 

 equal rays as for those with a group of regenerating rays. 



The evidence indicates that, most commonly, this starfish has 7 

 rays before it undergoes autotomy, that it divides into 3-ray and 4-ray 

 portions, and that each of these parts regenerates four rays. Regener- 

 ating rays tend to appear in bilaterally disposed pairs, as regards size. 

 There is no evidence that self-division occurs often in the life of 

 individuals, though possibly it does. New rays may be added at any 

 point on the disk. 



The number of madreporites varies from one to five, and is to some 

 extent correlated with the number of rays. It is not correlated with 

 the size of the animal. Double or triple madreporites occur in about 

 5 p.c. of the individuals. 



Notes on Holothurians.J — J. H. Orton makes a detailed contrast of 

 the specific characters of Cucumaria saxicola and G. normani ; the 

 differential characters of most importance being found in the main body 

 spicules, in the spicules near the surface of the body, in the shape and 

 number of the gonadial tubes, and in the shape and relative stoutness of 

 the pieces of the calcareous collar. The variation of the gonadial tubes 

 in G. saxicola is recorded ; the usual number is 2-1 or 25, but there is 

 variation between 10 and 61, between 10 and 33 in females, between 



* Ber. Nat. Ges. Freiburg, xx. (1914) pp. lxxv-xc (2 figs.). 



t Amer. Naturalist, xlix. (1915) pp. 28-36 (13 figs.). 



\ Journ. Marine Biol. Assoc, x. (1914) pp. 211-35 (13 figs.). 



