EDITH 1'INNEY. 



In Kjlo. before the appearance of Balt/er'- later paper. Miss 

 llciiiHT published observations made in this laboratory upon. 

 Toxopneustes i'<i>-i<':>ati<s, one of the American species \\hich has 

 pn>\rd -ii valuable in cross breeding experiments. 1 She found 

 in straight fertili/ed Toxopncit*: ; somatic pair ol long 



rod- approximating in length tin- long rods ol" Sphaer echinus. 

 II ill' of tli. eggs contain t\\o and half tlmv Y-shaped element-. 

 Tin- impaired Y is undoubtedly the accessory chromosome. The 

 chromosome number in 'ro.\-<>ficustes is thirty-six, the same as in 

 mgylocentrotus .md Echinus. Miss HelTner also examined 

 Arhddn pituctnlatii but found the eg^s unfavorable for di-taiK-d 

 c\ tolo-jcal -indy, a fact which forms another point of roemblunce 

 In tween the American and European specie- di-cribed. 



The present paper deals with two additional species of echi- 

 noid-, Ilipponni' csculcnla (Tripneustes csctilciitns) and Moini 

 titropos, M\- special object has lieen to determine whether any 

 or all of the chromosomes exhibit any of the various- expressions 

 of individuality which have been reported for the other form- 

 mentioned above. 



I am indebted to Dr. Tennent, at whose instance tin- work \\as 

 undertaken, for tin- material used and direction during the course 

 of ii- investigation. I wish also to express my gratitude to Dr. 

 Stevens for her interest and helpful suggestion-. 



Hipponoe esculenta. 



I'ln- Hif>()nn<H' material was collected and pre-erved at the 

 Tortu^a- laborator\- of the Carnegie Institution in the summers 

 of I'jo'i and [i)lo by Dr. Temu-nt. It was pn-parrd in the Usual 

 manner for study, the onlv -tain u-ed being Heidenhain's iron- 

 hsematoxylin. ( )b-er\ ation- made on tir-i and second cleavage 



-|iindle- form the chief ba-i- of my concln-ioiis. 



The character of the IIif)()nnot- spindle di-lax-ed somi-v, hat the 

 solution of the problem at hand. The cytoplasm of the e.^u is 

 bi-autifully clear and the chromosomes conijtared toother echin- 

 oderm chromosomes are of -ood size, but during di\i-ion tlu-N- 

 are so crouded on the spindle that the\ ob-cnre one another. 

 This may be attributed to several causes. It may be due to the 



1 Tcnnont. '07, ' i <m. ' i 06 .ml ' i i . 



