152 REPORTS ON INVESTIGATIONS AND PROJECTS. 



brane had been ruptured. In such cases it was found that the eupyrene sper- 

 matozoa swarmed around the egg, while the apyrene remained unstimulated. 



In February and March, in Jamaica, although the eggs of Strombus were 

 not yet ripe nor the ovary fully developed, the seminal receptacle was found 

 to be full of eupyrene spermatozoa, indicating that copulation had already 

 taken place. When mixed with water the spermatozoa soon became very 

 active. In no instances were any apyrene spermatozoa found in the seminal 

 receptacle. Occasional clusters of granules resembling those of the adult 

 apyrene spermatozoa were always present in the contents of the seminal 

 receptacle, but these probably came from ruptured secretory cells which line 

 its cavity. 



The condition of the testis of Strombus was such that it was possible to 

 study the developmental stages of the apyrene spermatozoa in the live condi- 

 tion. By so doing I was able to verify many figures that had been previously 

 drawn from sections of preserved material. 



In addition to Strombus, the dimorphic spermatozoa of Turbinella, Triton, 

 and Cassis were examined and material collected for purposes of comparison. 



Investigations on the Hybridisation of Hchinoids, by D. H. Tennent, 



Bryn Mawr College. 



During the first half of my stay at Montego Bay I reinvestigated reciprocal 

 Hippono'e and Toxopneustes crosses in order to ascertain whether the same 

 types of larvae were to be obtained in March as I had previously obtained at 

 Tortugas in June and July, such observations being desirable because of 

 those on seasonal variation made by Vernon and others. It may be said that, 

 in general, the Hippono'e influence, although pronounced, was less strongly 

 marked than in my previous experiments. A modification of skeletal struc- 

 ture was brought about by methods similar to those described in my article 

 in Publication No. 132 of the Carnegie Institution of Washington, 1911. 

 During the second half of my stay I obtained and studied material from 

 other crosses. 



I count myself especially fortunate in obtaining crosses between Cidaris 

 female and Hippono'e male and Toxopneustes male. A study of the normal 

 early development of Cidaris showed that, in this form, the mesenchyme is 

 formed very late, being given off during the gastrula stage from the inner 

 end of the archenteron about 26 hours after fertilization. In Hippono'e and 

 Toxopneustes the mesenchyme is formed much earlier, arising before gastru- 

 lation about 8 hours after fertilization. 



In the Cidaris female X Hippono'e male and Cidaris female X Toxo- 

 pneustes male crosses, the mesenchyme is formed slightly earlier than in the 

 straight development, the first mesenchyme cells appearing at the lips of the 

 blastopore at the base of the archenteron. The observation gives very con- 

 clusive evidence of the early influence of the foreign sperm on development. 



During my stay at Montego Bay I also obtained material for the following 

 cytological studies : 



(i) A further study of the Hippono'e female X Toxopneustes male 

 cross. 



(2) A further study of the same cross modified by the addition of 



N/io acetic acid. 



(3) A study of chemically fertilized Hippono'e eggs. 



(4) A study of normally fertilized Cidaris eggs. 



