SURVEY OF INVERTEBRATES 85 



microhiberculatus and Ophioderma longicauda hardly 

 survive a 24-liour exposure to anaerobic conditions. 



Thus, while no definite statement is possible at pres- 

 ent as to whether any adult echinoderm is able to lead 

 a completely anaerobic life for any length of time, it 

 appears safe to assume that a partial transition to an- 

 aerobic metabolism is possible in many cases. This is 

 indicated by the fact that the oxygen consumption of 

 various species is dependent on the tension, as has been 

 shown for the holothurians Caudina chilensis (Nomura, 

 1926) and Thy one briar eus (Hiestand, 1940), as well as 

 for the starfish Patiria miniata (Hyman, 1929), Asterias 

 rubens (Meyer, 1935) and Asterias forbesii (Maloeuf, 

 1937). 



Much more work has been done with the eggs and 

 sperms of echinoderms, especially of sea-urchins. Un- 

 fertilized eggs of Arbacia were kept for periods of five 

 to eight hours in the complete absence of oxygen (Har- 

 vey, 1930; Barron, 1932). This treatment did not de- 

 prive them of their ability of being fertilized after the 

 restoration of aerobic conditions. However, after 24 

 hours without oxygen many eggs were damaged and the 

 fertilization rate had decreased to 15 to 20 per cent. 



On the other hand, earlier observers, as for example, 

 Loeb and Lewis, 1902, Loeb, 1915 {c.f- also Lyon, 1902), 

 had reported that the fertilization rate of the Arbacia 

 egg was not affected at all after a 24-hour exposure to 

 hydrogen, and that some eggs could be fertilized even 

 after 64 hours. It is probable, as Barron (I.e.) points 

 out, that in these older experiments the oxygen was not 

 completely eliminated. 



The spermatozoa of the sea-urchins proved to be more 

 sensitive than the eggs, both in Barron's and in Harvey's 

 experiments. They became rapidly immobilized and lost 

 the power of fertilizing normal, untreated eggs when they 

 had been kept for 3 hours under hydrogen. 



