128 Papers from the Marine Biological Laboratory at Tortugas. 



type. Vernon concluded that this variation was due to the relative 

 maturity of eggs and sperm. 



Besides this major conclusion, two minor conclusions are of im- 

 portance: 



(1) Respecting reciprocal crosses; 9 out of 13 possible reciprocal 

 crosses were attempted, from which, plutei were obtained from both 

 crosses in 7 instances. Vernon concluded that "The capacity for recip- 

 rocal crossing seems, therefore, to be the rule rather than the exception." 



(2) Respecting the Hertwigs' conclusion with regard to cross-fertili- 

 zation and the staleness of the eggs, he confirmed the observations as to 

 fertilization itself, but decided that there was a less tendency for such 

 stale eggs to develop to plutei than for eggs fertilized in a fresh condition. 



Herbst (1906, 1907) had little faith in the idea of a greater or lesser 

 ripeness of reproductive elements and sought for another controlling 

 factor. "Das ist aber fur unsern Zweck ein erfreuliches Resultat, denn 

 jetzt ist die Moglichkeit vorhanden, dass wir an Stelle des dunklen innern 

 Faktors der verschiedenen Reife einen scharf prazisierbaren ausseren 

 in die Hand bekommen konnen, von dem die Ausgestaltung der Bas- 

 tarde abhangig ist," expresses his attitude towards the question. He 

 suggested, as possible means of control, change in temperature, change 

 in salt-content, or change in concentration of OH ions, the last of which 

 might be connected with the presence of larger or smaller quantities 

 of algas or connected with the reserve-stuff content of the eggs, which 

 would be dependent on variation in the interaction of sea-urchin and 

 environment. 



Herbst selected the skeleton as the character for study. In his 

 investigations with Sphcer echinus 9 X Echinus of 1 and Sphcerechinus $ X 

 Strongylocentrotus cT he considered in detail the effect of changes in tem- 

 perature on the character of the skeletal rods of the anal arms and on 

 the number of "roots" of anal arm supports, defining these roots as 

 any outgrowth from the horizontal part of the oral bar, anal crossbar, 

 or body-skeleton directed into the anal arm. 



For the purpose of comparing Herbst's results with my own I 

 include parts of four of Herbst's tables, Nos. Ill, VI, X, and XII (1906, 

 pages 192, 203, 225, 230). 



Temp. Temp. 



Herbst's Table III - ........................................ 1 1 to 19 C. 24 to 27 C. 



Number of plutei with lattice structure ......................... 19 37 



Number of arms with lattice structure .......................... 24 53 



Number of arms with multiple bars ............................ 28 5 



Temp. Temp. 



Herbst's Table VI. g tr ' ^ ........... ntoi9C. 2 4 to2 7 iC. 



Sph. 9- 



Anal arm rods with i root ..................................... 35 i 



Anal arm rods without lattice str ............................... 24 5 



Anal arm rods with 2 roots .................................... 54 54 



Anal arm rods with 3 roots .................................... 10 27 



Anal arm rods with 4 roots .................................... 0.6 9 



Temp. Temp. 

 Herbst's Table X, ^ ........................................ ii toi 9 C. 23 to 29 C. 



Number of plutei with lattice structure ......................... 12 37 



Number of arms with lattice structure .......................... 19 54 



Number of arms with multiple bars ............................ 28 15 



