Transmission electron microscopy (TEM) has an irreplaceable role in the imaging of biological samples and is gaining greater importance in actually visualising and verifying processes that are hypothesised based on emerging molecular studies. Hence, the requested ultramicrotome—to prepare high-quality and uniform serial selections—is an indispensable and durable complement to several lines of vastly evolving, innovative research. One specific research objective elaborated in the current project is to obtain insight into the diversity and evolution of spermatogenesis and sperm in nematodes. Firstly, we will investigate the spermatogenesis of several unexplored nematode taxa by TEM, including immunostaining of specific proteins. The selected research organisms are key taxa (from an evolutionary point of view) and will expand our knowledge to increasingly distant relatives of the model organism Caenorhabditis elegans, which is not a representative of all nematodes. Secondly, the newly obtained and already available information on spermatogenesis will be combined in a phylogenetic framework for the first time. Because phylogenetic trees preserve traces of the historical evolutionary processes that gave rise to the diversity of contemporary species, the combination of a phylogeny and information on species can be used to infer what the past was like and how the present came about. By doing so, we will be able to reconstruct the precise sequence of evolutionary changes, essentially to understand a complex phenomenon such as spermatogenesis. Further correlations of spermatogenesis traits with other different properties, such as life history or habitat specificity, will be valuable to our understanding of the process of selection and neutral evolution in spermatogenesis.