I2O W. C. ALLEE. 



I. 



EMBRYOLOGY OF RHYNCHOBOTHRIUM : DR. R. H. BOWEN. 



Take from the spiral valve of the dogfish the ripe, free, milk- 

 white proglottids of Rhynchobothrium and place them in finger 

 bowls of fresh sea water ; ten or a dozen may be put in one bowl. 

 Care should be taken not to carry over too much of the digestive 

 slime as it is not feasible to change the water once the eggs are 

 laid. If the proglottids are ripe they discharge the eggs at once 

 in a white cloud. The empty proglottids should be removed and 

 the finger bowl set aside without agitating the water. The eggs 

 soon become dark brown or blackish and stick together and to the 

 bottom of the dish in a solid mass. By keeping the eggs thus 

 bunched their concentration can be controlled when removing 

 them for study. Fresh eggs can be examined at once after lay- 

 ing, but they offer nothing of special interest. After not less 

 than three days and up to periods of five to six days, the hexa- 

 canth embryos are completed and ready to emerge from the egg 

 cases. Remove a part of the cluster of eggs by scraping them off 

 and sucking up in a pipette and examine under the microscope. 

 The mechanical disturbance of moving them seems to stimulate 

 the embryos, for it is usually easy to find a number of embryos 

 just emerging from the egg-cases ; also free swimming embryos 

 and empty egg-cases. Cultures four days old are generally the 

 best. 



I 



II. 



APPROXIMATE SCHEDULE FOR STAGES IN ECHINODERM DEVELOP- 

 MENT UNDER MID-JULY CONDITIONS, FROM THE EXPERI- 

 ENCE OF Miss CHRISTIANNA SMITH. 



i. Asterias forbesi. 

 Stages. Time after Fertilization. 



Polar body formation 45-60 minutes. 



Two celled 2-3 hours. 



Four to eight celled 3-4 hours. 



Sixteen celled 4-5 hours. 



Late blastula 710 hours. 



Early gastrula 18-21 hours. 



Late gastrula 24-30 hours. 



