This
is the same image in a slightly different format, with five different kinds
of organelles labelled as follows:-
pg - are the pigment granules, which reduce stray light through the eye. These organelles featured in the picture quiz for February and are prominent features in the retinula cells themselves, as well as special pigment cells at the sides of the eye.
mit - are the mitochondria, incredibly highly specialised and with an intriguing evolutionary history - as featured in the March quiz.
gc - is a Golgi complex, here seen inside the retinula cells, but previously described in the lentigen cells.
er - the endoplasmic reticulum. This comes in two varieties: smooth and rough. In simple terms, smooth er may be associated with the Golgi apparatus and is generally involved in transport of materials through the cell. Rough er is so-called because its membranes are studded with electron-dense particles. These particles are the ribosomes, very important in the synthesis of proteins. They form part of the information-processing system linking the DNA in the nucleus (containing the genotype) via RNA controlling the sequences of amino acids that make up the protein molecules and thus, directly or indirectly, the observed properties of the cell (and of the organism of which it forms a part, i.e. the phenotype).
mvb - multivesicular body. Possibly a kind of lysosome - of which more at a later date...
pm - is the plasma membrane = the cell membrane. The magnification in this image is two low, but typically the plasma membrane has a two-layered structure based upon a lipid bilayer coated with proteins and carbohydrates and with protein molecules embedded within the layers of lipid molecules. Foldings of this membrane produce the microvilli which make up the rhabdom of the retinula - as shown in the quiz for December.
For further details, see:
Curtis, D.J. (1970) Comparative aspects of the fine structure of the
eyes of Phalangida (Arachnida) and certain correlations with habitat. J.
Zool., Lond. 160: 231-265.
and
Curtis, D.J. (1969) The fine structure of photoreceptors in Mitopus
morio (Phalangida). J. Cell Sci., 4: 327-351.
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