For each topic, a limited number of images from the chronological travel presentations that have a certain coherence, have been brought together in order to reflect the diversity of a subject. It is not necessarily the intention to be even somewhat complete within such a 'theme'. For example, if 'Monkeys' has six images, you cannot conclude that there are exactly six images of monkeys on the site (there are many more).
Various images also contain a link that allows you to go to the point in the journey where that image plays a role. Sometimes you find more material around that point in the journey that deals with that theme, but sometimes it concerns a subject that only played a small role in that journey.
The main function of the links is actually 'random surfing' to a fairly random point in a fairly random journey so that you can be surprised by something that you would not have gotten to so quickly due to all the choices.