Drosophila ovaries! 

So beautiful.

I worked extensively with ovaries as a genetic model system during my PhD, in which I contributed to the characterisation of a novel protein family that is evolutionarily conserved between flies and all higher mammalian systems, including humans. I actually got to name the gene that represents this family! It's called "pickled eggs", or "pigs" for short, to describe the 'broken egg' phenotype which was very obvious when I looked at 'null mutant' ovaries for the first time (from flies in which I 'deleted' the gene).

The Drosophila egg chamber is a well-established model in developmental biology. Female Drosophila have two ovaries, each containing of roughly 16 ovarioles. The ovariole is a string of 6 or 7 sequentially developing egg chambers, or developing eggs; at the small end, reside 2-3 stem cells; at the large end, the mature egg. Ovarioles comprise several types of cells, including 'germline', 'somatic' and stem cells, and are a well-established model system to study cell adhesion, cell cycle regulation, cell differentiation, cell polarity, endocytosis, exocytosis, morphogenesis, cancer metastasis, developmental patterning and too many other processes to list here! 

10x magnification. Confocal micrograph.

(For aficionados, the yellow cellular component labelled here is EB1, a microtubule +-tip tracker.)

Imaged using an Olympus Fluoview 1000 in the laboratory of my gracious mentor, Dr Nick Brown (Cambridge University), with funding from the BBSRC, and gratitude to my PhD supervisor, Dr Katja Roper (MRC-LMB, Cambridge University).