186 CARNEGIE INSTITUTION OF WASHINGTON. 



In order to supplement certain conclusions stated in his great work 

 on the "Phylogeny of the Echini," Professor Robert Tracy Jackson 

 collected 2,878 specimens of echini at Montego Bay, Jamaica, and 

 studied the changes in position of their ocular plates during the 

 growth of the individual. He found, in conformity with his previous 

 conclusions, that primitive and geologically ancient genera, such as 

 Centr echinus, are very slow in acquiring the final arrangement of ocular 

 plates, whereas more recent and highly specialized genera, such as 

 Strongylocentrotus, have a highly accelerated development. This is in 

 accord with Hyatt's observations on fossil cephalopods. Changes 

 which are significant in relation to the phylogenetic status of the 

 group occur throughout the life of the individual, as Dr. Jackson has 

 shown both in his studies upon plants and upon echini. 



Dr. Merkel H. Jacobs, basing his conclusions upon a study of the 

 reactions of four species of parasites which inhabit the alimentary 

 tract of one of the echini, decides that the physiological characters of 

 an organism are not merely the result of its environment, but may be 

 as fundamental and characteristic as its morphological ones. 



Dr. H. E. Jordan came to Jamaica to study the cytology of the sex- 

 cells of Echinaster, but as no ripe eggs could be obtained from these 

 star-fishes, he studied the spermatogenesis of the mongoose, and con- 

 cludes that in mammals in which an x-element is present the female sex 

 is homozygous and the male heterozygous. Apparently the accessory 

 chromosome acts as a deterrent to the development of maleness. 



Professor W. H. Longley's researches have been referred to elsewhere 

 in this report. 



Dr. J. F. McClendon, upon testing their electrical conductivity by 

 Kohlrausch's method, found that the permeability of echinoderm eggs 

 to ions increases on fertilization. The unfertilized egg is perhaps in a 

 dormant condition, and the increase in permeability probably allows 

 a rapid interchange with the surrounding medium necessary for 

 activity and development. 



Alfred G. Mayer found that the more specialized sort of cilia, which 

 move intermittently at regular intervals of time, are affected by the 

 cations of sea-water in a manner which is the converse of their effects 

 upon the neuro-muscular system. This is a mechanical, not a chemi- 

 cal, matter, for the cilia-bearing cells are very sensitive to pressure; 

 hence magnesium, which relaxes the muscular tonus and relieves the 

 skin-pressure, permits the cilia to beat at an abnormally rapid rate, 

 whereas sodium, which causes the muscles to contract, increases the 

 muscular tonus, and hence the pressure upon the cilia-bearing cells is 

 increased and the cilia cease to beat. 



Pressure also dulls the sensitiveness of the neuro-muscular system of 

 Cassiopea, and neurogenic contraction waves always travel from un- 

 pressed to pressed regions, w^hether from anode to cathode or from 

 cathode to anode, provided one electrode presses upon the tissue 



