140 Papers from the Marine Biological Laboratory at Tortugas. 



Good fertilization membranes were formed. A high percentage of 

 cleavage was obtained, but the cleavage was irregular. 



(4) Toxopneustes eggs treated with ^^ NaOH (2 c.c. to 100 c.c. 

 sea-water) for 3 minutes and then fertilized with Holothuria sperm. 

 Most of the eggs were destroyed by the entrance of the sperm. 



(5) Toxopneustes eggs treated with fm CaClj (2 c.c. to 100 c.c. sea- 

 water) for 5 minutes and fertilized with Holothuria sperm 45 minutes 



Fig. 6. — Parthenogenetic 



Sphcerechinus pluteus 



(Herbst). 



Fig. 7. — Strongylocentrotus 

 pluteus 

 (Herbst). 



after transference to sea-water. A fertilization membrane was formed 

 at once. Most of the eggs then burst. A few gave good segmentation. 

 In the eggs treated with fm CaClj and with ^"^ NaOH the sperm 

 upon entering, in most cases, tears the egg to pieces. A deep notch or 

 pathway made by the sperm may be seen and then the egg suddenly 

 disintegrates. In this connection it is interesting to note that the Holo- 

 thuria floridana egg has a very thick membrane and a well-defined 

 micropyle. 



Mellita: 



The Mellita Q X Moira o" cross was easily made. About 10 per cent 

 of the eggs were fertilized after being well washed in sea-water. Most 

 of the plutei were of the intermediate maternal type with multiple rods 

 in the anal arm. A few were of a well-marked maternal form (plate 2, 

 fig- 23), yet showing evidences of the hybrid origin. The body was 

 rounded posteriorly, but the skeletal basket was absent. There was no 

 trace of the posterior unpaired spine, the Moira character which it was 

 hoped would appear. 



