Light Organ
The light organ has an electrical response when stimulated by light, which suggests that the organ functions as a photoreceptor that enables the host squid to respond to V. fischeri's luminescence.
Extra-ocular vesicles collaborate with the eyes to monitor the down-welling light and light created from counter-illumination, so as the squid moves to various depths it can maintain the proper level of output light. Acting on this information, the squid can then adjust the intensity of the bioluminescence by modifying the ink sac, which functions as a diaphragm around the light organ. Furthermore, the light organ contains a network of unique reflector and lens tissues that help reflect and focus the light ventrally through the mantle.
The light organ of embryonic and juvenile squids has a striking anatomical similarity to an eye and expresses several genes similar to those involved in eye development in mammalian embryos (e.g. eya, dac) which indicates that squid eyes and squid light organs may be formed using the same developmental "toolkit".
As the down-welling light increases or decreases, the squid is able to adjust luminescence accordingly, even over multiple cycles of light intensity.
Read more about this topic: Euprymna Scolopes
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