Ultrastructure of the spermatozoon ofElenchus japonicus and its bearing on the phylogeny of strepsiptera.

The fine structure of the mature spermatozoon of the strepsipteranElenchus japonicus Esaki and Hashimoto (Elenchidae) is described using transmission electron microscopy. The spermatozoon was seen to have an elongated head, a tail containing a 9 + 9 + 2 axoneme, two mitochondrial derivatives and two accessory sheaths. The monolayered acrosome is conical in shape while the nucleus exhibits an internal channel of uncondensed chromatin. The tail is long, and in its final portion, the axoneme, loses its elements progressively. These results are compared with the sperm ultrastructure ofXenos moutoni De Buysson (Stylopidae) and with those of other insect orders, particularly the Coleoptera.