For the last 3 days I have been dissecting a small land snail, an enid species (family Enidae) from Turkey. The picture below shows the entire body of the snail with nothing removed except its shell, most of which I dissolved away with acetic acid (I forgot to take pictures during that process). The twisted mass of white tubes on top of the body is the snail's genitalia.
The examinations of the genitalia help us distinguish between species. Evolution usually creates anatomical differences between the genitalia of different species. Such differences may decrease or completely prevent the mating of closely related species, thus, contributing to their evolutionary divergence.
The removal of the genitalia from small snails is not easy, requiring a lot of patient, careful cutting and teasing apart of tissues by a pair of steady hands manipulating tweezers with very fine tips. I do most of my dissections late at nite when I am relaxed and slightly sleepy after a bottle of beer.
The scale is in millimeters.
In the picture below the main mass of the reproductive organs of the snail is on the left, while the rest of the body is on the right. Obviously, the reproductive organs make up a significant portion of the overall body mass. That being the case, their energy requirement-during reproduction-must also be a significant fraction of the total energy budget of the snail.
The diversion of resources from one organ system with a high energy requirement to another organ system also with a high energy requirement must be one process that creates trade-offs during evolution. For example, when the members of a population of a snail species starts making thicker shells, they may become less vulnerable to predators. But at the same time, their reproduction may slow down and the number of offspring may go down. This compensatory trade-off arises, because energy and resources may have to be channelled from reproduction to shell-making. Ultimately, it is up to natural selection to pick between thicker shells or more offspring.
I still have to untangle the penis, epiphallus, appendix, vagina, etc., from each other without breaking anything apart and then spread them out and pin them down for examination and further photography.