410 S. J. HOLMES 



fL Jordan (17) has studied in detail the function of the con- 

 tractile fibers of the body wall of holothurians. Holothurians, 

 actinians, annelid worms and many other forms are grouped in 

 a division which Jordan calls hollow organ animals. In these 

 forms the absence of internal or external skeleton is in a way 

 compensated for by the presence of fluids within the animal 

 which, when under pressure, afford a certain rigidity to the 

 body. There is a detailed study of the general physiological 

 properties of the muscles of holothurians as well as certain 

 fibers of the skin which while different from other muscle fibers 

 are shown to be contractile. These latter Jordan thinks have 

 a special function of maintaining the tonus of the body, while 

 all the more nearly typical muscles have their function limited 

 to simple contractility. There is thus a separation of functions 

 performed by striated muscles of higher forms similar to that 

 which Von Uexkiill describes for the two sets of fibers supply- 

 ing the spines of the sea urchin. 



Just (18) finds that at Woods Hole, Massachusetts, the swim- 

 ming of Platynereis me galops occurs in July and August in the 

 dark of the moon. The breeding activities may be studied in 

 the laboratory although the males are rather delicate and as a 

 rule live only a few days in receptacles of sea water. The male 

 in swimming coils spirally about the body of the female and 

 works forward until he gets into a position in which the female 

 may seize his tail in her jaws. Just thinks that the sperms 

 are swallowed by the female and fertilize the eggs internally, 

 after which ovulation takes place by the rupture of the body 

 wall. After copulation sperm may be found in the pharynx 

 " whence they escape through lesions in the pharyngeal wall to 

 the coelom." 



Kafka (19) has given a valuable and welcome summary of 

 work on the sensory reactions of the invertebrates. 



Kanda (20) finds that the anterior end of Paramecium cau- 

 datum and Spirorostum teres is heavier than the posterior end 

 and therefore the orientation to gravity shown by these forms 

 cannot be a merely mechanical one. Differences in pressure of 

 water on the two ends or sides of the body are so slight as to 

 be negligible, and besides both these forms orient negatively to 

 gravity in solutions of greater specific gravity than their body. 



