go THE AMERICAN ARBACIA 



b. Swimming Rate 



The swimming rate of the Arbacia punctulata spermatozoon is, according 

 to Grave and Downing (1928) and Grave (1934), about i mm. per 

 minute at 22.5° C., or 20 times its length (50 \x) per minute, and 

 slightly faster at a higher temperature. Gemmill (1900) gives a little 

 higher rate for Echinus esculentus. For Psammechinus miliaris, with a 

 slightly different technique, Rothschild (1951a) estimates 200 [x per 

 second (translatory speed), or about 12 mm. per minute at 18° C. 



The human sperm swims, in the uterus and Fallopian tube (a 

 distance of about 190 mm.), at the average rate of about 2.7 mm. per 

 minute (R. L, Brown, 1944) or about 45 times its own length (60 [i] 

 in one minute. A good swimmer swims a mile in 20 minutes, so that 

 a six-foot man swims 44 times his own length in one minute. A human 

 sperm and a man thus swim at about the same rate, length for length 

 (E. B. Harvey, 1946b). 



For a further comparison, a gastrula of Arbacia lixula, whose dia- 

 meter is approximately 0.2 mm., swims in a tube of its own diameter 

 according to Needham ( 1 93 1 , Vol. 2, p. 1 247) at the rate of i . 1 7 meters 

 per hour, or 20 mm. per minute, 100 times its diameter. The Arbacia 

 lixula gastrula swims about 20 times as fast as the Arbacia punctulata 

 sperm, or 5 times as fast, length for diameter. A greater rate would be 

 expected on account of the numerous organs of propulsion, the cilia, 

 though it is not as streamlined. Paramoecium caudatum swims about 

 3 mm. per second or 15 times its length (ca. 200 {i) according to Lud- 

 wig (1928); this makes the rate about 180 mm. per minute or 900 

 times its length. Paramoecium therefore swims nine times as fast as the 

 gastrula of ^. lixula. This greater rate might be expected since Para- 

 moecium caudatum is streamlined. Other rates have been given for Para- 

 moecium by other investigators. Tabulae Biologicae (IV p. 480, Metzner, 

 1927) give 1.3 mm. per second for P. caudatum, length 216 [x. Chase and 

 Glaser (1930) give 833 p. per second, species not mentioned but proba- 

 bly P. caudatum. Wichterman (personal communication 1953) has 

 found that for a given species, the rate varies with the phase in its 

 growth and life cycle. 



c. Motility 



The effect of dilution in activating the sperm and the loss of fertiUzing 

 power with time have been studied in Arbacia punctulata by F. R. Lillie 

 (1915 b), though they were observed earlier in Echinus esculentus by 



