This is the 38th of 100 lithographs designed by Haeckel for his depiction of beauty in nature through his body of work named "Kunstformen der Natur". It was originally published in sets of ten between 1899 and 1904 and all of the sets combined later became a single book. The prints show various organisms, many of which were first discovered and described by Haeckel himself.
On this print you can see the numbers next to each organism and they are:
1-2 Periphylla mirabilis - named by Ernst Haeckel with 1 being the cross-section of the organism and 2 the view from the side
3 Periphylla Peronii - also named by Haeckel
4 Periphylla hyacinthina
5 Periphylla mirabilis - named by Haeckel