Chaetognaths are traditionally classed as deuterostomes by embryologists. Cohen also pioneered the use of micromanipulation techniques that are now widespread among embryologists. Fertility clinics are staffed with trained personnel including reproductive endocrinologists, embryologists, sonographers, and nurses. However, some modern molecular embryologists suggest that recent findings support the idea of inversion. Some embryologists postulate that the ostium secundum may be formed through programmed cell death. However, anti-vitalist experimental physiologists and embryologists, especially in Europe, were increasingly influential.