For years the motility of the male sex cells has been considered the chief or even sole criterion by which to judge the fertility of the male. It is too often forgotten, however, that motility is not even an inherent attribute of the spermatozoa, and Schücking1 believes that in some animals with external fertilization the sperms, themselves not motile, may be brought to the ovum by external circumstances and then fertilize it. This is contradicted by others,2 but the fact that such a difference of opinion can occur shows that motility alone must not be rated too highly. There are other characteristics of the sperm cells which are just as important as motility, as I3 have brought out before in previous articles.
In animals with internal fertilization the spermatozoa, of course, need motility to reach the ovum, but the degree of motility present under the microscope in
MOENCH GL. EVALUATION OF THE MOTILITY OF THE SPERMATOZOA. JAMA. 1930;94(7):478–480. doi:10.1001/jama.1930.02710330032010