Scorpions use sclerotized spermatophores for sperm transfer. The family Bothriuridae has one of the most complex scorpion spermatophores, with a distinct capsule and lamella. This study evaluates the viability of hypotheses relating to the evolution of animal genitalia that attempt to explain the functional morphology observed in spermatophores and female genitalia of some members of this scorpion family. These hypotheses are: female choice (internal courtship), conflict of interests (morphologically forced insemination) and lock-and-key (interspecific mechanical incompatibility). Observations of the mating sequences of 13 bothriurid and one buthid scorpion were recorded. The histology of female atrium was analysed. The data suggest that: (1) a genital copulatory courtship (sexual stimulation through male genitalia) could be a widespread mechanism among the capsules of the studied spermatophores; the wall of the female genital atrium in Brachistosternus as well as of other genera is usually rubbed by spines, tubercles or capsular lobes of spermatophores; the female genital atrium is relatively soft, elastic and uniform among different species; (2) morphological coercion might be admissible only when capsular lobes are very well developed, as females will have difficulty in disengaging by themselves from the large lobes if they attempt to interrupt sperm transfer; this mainly occurs in Bothriurus bonariensis; (3) observations of matings among closely related species indicate that the lock-and-key hypothesis is unable to explain spermatophore morphology in the studied species; however a certain degree of mechanical incompatibility occurs during interspecific mating between two sister species (B. bonariensis and B. chacoensis) owing to differences in capsular lobes and post-insemination behaviour; (4) these hypotheses might not be directly applied to simple spermatophores of the Buthidae Zabius fuscus. The results indicate that even though one genital mechanism can be more frequent than others, they can also exist together, not only in different genera but also in a single species (e.g. simultaneous occurrence of genital sexual stimulation and genital coercion in B. bonariensis). Indirectly these data suggest that the hypotheses most frequently quoted to explain genital morphology are not mutually exclusive.

Genital mechanics are studied in five species from three genera of neotropical pholcid spiders. The study focuses on the function of a pointed and upward projecting (‘pup’) apophysis on the male pedipalpal femur: it engages an indentation in the genital bulb during copulation. This character is geographically restricted to spiders in Central and North America and the West Indies and is considered a key character of the monophyletic ‘Modisimus group’. This includes the genera Modisimus Simon, 1893, Psilochorus Simon, 1893, Bryantina Brignoli, 1985, Anopsicus Chamberlin & Ivie, 1938, and some species now misplaced in Coryssocnemis Simon, 1893 and Blechroscelis Simon, 1893. Evidence for the polyphyly of the following genera is presented: Psilochorus, Coryssocnemis, and Blechroscelis. Some notes on the reproductive biology of the species studied are briefly presented.