126 Papers from the Marine Biological Laboratory at Tortugas. 



7.4 per cent smaller; green light, 4.8 per cent smaller; red light, 6.9 

 per cent smaller; yellow light, 8.g per cent smaller. 



The body length was uninflvienced by the number of larvae in a 

 given volume of sea -water, provided this number be kept below 30,000 

 per liter. It was also uninfluenced by the amount of sperm added on 

 impregnation. Larvae grown in water containing an additional amount 

 of carbonic acid were slightly larger than normal. 



The larvae were not much influenced by partial de-aeration or by 

 oxygenation of the water in which they were developing. 



The aboral and oral arms reached their maximum length after 8 

 days' development, after which they underwent absorption. The body 

 length increased regularly up to the sixteenth day. The arms of larvae 

 impregnated at 8° were 8 per cent shorter than normal; at 25° about 2.5 

 per cent shorter. In larvae developed above 22° the aboral and oral 

 arms were respectively 10.8 per cent and 8.5 per cent longer than those 

 developed at 18° to 20°. The body length of larvae developed in diluted 

 water was increased on an average by 9.1 per cent, while the arm lengths 

 were increased by 7.7 per cent and 10.5 per cent. The absolute arm 

 lengths were not affected. Arm lengths in darkness, semi-darkness, 

 green and violet lights were 10 per cent or more shorter than those grown 

 under normal conditions. 



The variability of larvae with respect to body lengths decUned after 

 the fifth day. The variability reached a maximum at 18° to 20°, the 

 temperature most favorable to development. 



In this work Vernon notes the common occurrence of multiple rods 

 in the anal arms, this variation sometimes reaching 35 per cent. 



Vernon (1898) determined the specificity of reaction to temperature 

 in Strongylocentrotus , Sphcer echinus, and Echinus : The Strongylocen- 

 trotus pluteus body was largest at 23.7°; the SphcBr echinus pluteus body 

 at 15.9°; the Echinus pluteus body at 20.4°. 



Steinbriick's (1902) study of Strongylocentrotus showed that the 

 occurrence of multiple rods in the anal arms is a common variation. 

 In a study of Toxopneustes (Tennent 19 10) I have shown in the purely 

 bred larvae a type or line variation and the tendency of the eggs of a 

 given female to vary as a whole in some direction. Hagedoom (1909) 

 has shown the common occurrence of similar variations in the skeleton 

 of Strongylocentrotus purpuratus. 



Herbert's (1906) research on purely bred larvae seems to have escaped 

 the attention of most investigators. He subjected embryos Echinus 

 Sphcerechinus and Strongylocentrotus to temperature changes. 



For Echinus he notes with increased temperature : (i) A striking 

 increase in the number of multiple rods. (2) The average body length at 

 24° to 25.75° is less than at lower temperature. (3) The average arm 

 length is longer than at lower temperatures. (4) In frequent cases the 

 beginning of lattice formation. 



For Sphcerechinus he notes with increased temperature: (i) An in- 

 crease of multiple rods. The number of rods may be increased one or 

 two and in infrequent cases from three to six; but the number of rods 

 w^hich reach entirely to the end of the arm is raised only about one. 



