When within the testicular cyst, individual, immature sperm of Lestes sponsa acquire a cap of periacrosomal material. During passage through the spermiducts and vas deferens, the caps of individual sperm coalesce, producing clusters of sperm under a common cap. In Calopteryx virgo, entire sperm cells become embedded in an extracellular homogeneous substance. The joining substance in both species appear to be derived from decomposed surplus cytoplasm sloughed off from developing spermatids. The epithelial lining of the spermiducts adds secretions to this. Clustering of sperm cells was not demonstrated in species of the Coenagrionidae.