wtf-scientific-papers:[The lack of obvious secondary sex characters makes it difficult to ascertain
wtf-scientific-papers:[The lack of obvious secondary sex characters makes it difficult to ascertain the sex of monk seals in the field. If a seal is not lying with the ventral surface exposed, it can usually be made to roll over on its side by poking it sharply with a stick. Thus, under field conditions, it is practicable to identify sex of only a small number of seals.]Kenyon and Rice (1959) -- source link