THE INVERTEBRATE COURSE. 107 



over night. If time permits a half day is also spent on the com- 

 mon rotifers since no other place is available for this neglected 

 group. 



Echinodermq. Four days, lectures and laboratory. At present 

 this work is introduced by a day's study of maturation, fertiliza- 

 tion, cleavage and development stages of the starfish egg, with 

 sea-urchin and; sand-dollar material in reserve in case of need. 

 Approximate schedules for different stages in the development of 

 Asterias, Arbacia and; Echinarachnias, as worked out by Miss 

 Christianna Smith, are given in the appendix (II.). Preparation 

 for this day's work takes much time and careful cooperation with 

 Mr. Gray in the matter of securing plenty of ripe starfish, since 

 this is near the end of their breeding season. 



Work on the adult starfish begins with a study of the activities 

 of the living animal, which includes an annual repetition of Cole's 

 experiments on righting reactions and locomotion j 1 in spite of 

 diffuse lighting and class technique, these have on the whole sup- 

 ported Cole's contention that there is evidence of physiological 

 asymmetry in the starfish. The free cells in the ccelomic fluid are 

 also studied. We obtain these easily by hanging the starfish up 

 by one arm, catching a drop of the fluid as it escapes and examin- 

 ing immediately before aggregation takes place. Circulation in 

 the coelomic fluid and the dermal branchiae is demonstrated by 

 means of carmine injection. 



The sea-urchin takes more than a day for dissection even 

 though little time is spent on the arrangement of plates in the test. 

 Aristotle's lantern is studied in detail and the genital rachis in 

 Strongylocentrotus is dissected. For this work specimens pre- 

 served in alcohol are used. The dissection is made by picking off 

 the skeleton in the equatorial region, leaving one ray intact. The 

 exposure is gradually extended to the dorsal region, which is 

 held up as long as desired by the part of the shell still intact. 

 This gives better results than the classical method of dissection. 



Ophiodeniia and Leptosynapta are present in reserve for those 

 who have done the regular work. The latter are kept from the 



i " Experiments on Coordination and Righting in ihe Starfish," BIOL. BCLL., 

 24, 1913. "Direction of Locomotion in the Starfish," Jour. E.vp. Zool., 14, 



