Studies on the fine structure of the dorsal vessel of arthropods

Summary The beetle family Altioidae contains some very archaic surviving species, and at the same time, very modern ones. In one lineage from archaic to modern (Fornterita — Alticini — Oedionychini), the number of spermatozoa has been stepwise (according to a geometric series, 2ⁿ) reduced from 256 to 16 per bundle. Comparison with the relatively few data in literature show that this trend is common in insects: more archaic orders have more sperm cells per bundle than the more modern ones, and within an order, the most modern or most specialized groups tend to have least. The reduced number of spermatozoa per bundle may be a sign of reduced sperm production in general, and this probably has adaptive value in limiting genetic variability.A small number of spermatozoa per bundle is sometimes accompanied by an extra large size of spermatocytes. Except for the alticid subtribe Oedionychina, it is hard to see what adaptive value this could have. In the Oedionychines, the large size of the spermatocytes is a prerequisition for the evolution of gigantism of the asynaptic sex chromosomes.Partly supported by a grant (GB-4522) from the National Science Foundation (Washington).I wish to express my gratitude to Prof. Dr. Jan Bechyné, Instituto de Zoología Agrícola, Universidad Central de Venezuela, Maracay, Venezuela, for identification of most alticids mentioned in this paper.     

Morphogenesis of the decapitated and decaudated sperm defect in two brothers

The “decapitated sperm” defect, found in both of two sterile brothers, may be assumed to have a genetic origin. The present material suggests that the term “decapitated spermatozoa” is not exact, because detached heads and tails were found in the brothers' ejaculate that could be regarded as “decapitated tails” and “decaudated heads.” The present report describes frequent, more or less advanced stages of detachment. Both heads and tails showed a normal structure in which only the postnuclear region was deficient, lacking basal plate and implantation fossa. A break at a different level of the midpiece, and therefore three kinds of separation, were observed. The defect, according to the present research, must originate in the testicular region, whereas the detachment occurs in the epididymis.     

Spermatozoa and relationships in Palaeognath birds

In this paper the authors describe the ultrastructure of the mature spermatozoon and the spermatid in Struthio camelus and Dromaius novaehollandiae. The first species is characterized by a rod-like perforatorium within an endonuclear canal in the anterior third of the nucleus, while the second is characterized by an extremely reduced completely extranuclear perforatorium. Other differences are in the sperm dimensions, the number of mitochondria and the length of the axonemal accessory fibers. Considering both the present data and previous findings, Palaeognath birds appear to be a peculiar and monophyletic group, characterized by: 1), a conical acrosome surrounding the nucleus; 2), a fibrous sheath around most of the axoneme; and 3), an elongated distal centriole occupying the entire midpiece. Within this group, Tinamiformes seem to be more primitive than Struthioniformes. In the latter order Dromaius is distinctly different from the reduced Struthio and Rhea which are closely related to one another by the presence of a rod-like endonuclear perforatorium.