The scientists examined the shape of sperm from two types of squirrel monkeys, S. collinsi and S. vanzolinii, to learn more about these species and improve reproductive techniques. They collected sperm from both types of monkeys and analyzed it. They found that S. collinsi's sperm quality varied, with some having good quality and others not. Sperm with better quality had normal shapes. Poor-quality sperm had smaller, more oval heads. S. vanzolinii's sperm had larger heads than S. collinsi's but similar tail lengths. The shape of the sperm could predict the sperm's ability to move and its strength in S. collinsi. By studying S. collinsi, insights can be gained for S. vanzolinii.