GREGARINAE • DICCIONARIO INGLES.COM • Definition of Gregarinae

... nature, really nothing more than permanent ova. There are independent unicellular organisms of the simplest character which develop no further, but reproduce themselves as such, without any further growth. We know to-day of a great number of these little beings, such as the gregarinae, flagellata, acineta, infusoria, etc. However, there is one of them that has an especial interest for us, because it at once suggests itself when we raise our question, and it must be regarded as the unicellular being that approaches ...

— The Evolution of Man, V.1. • Ernst Haeckel