Sri Aurobindo
Letters on Yoga
5. Planes and Parts of the Being
When we speak of Purusha in the head, heart, etc., we are using a figure. The Muladhara from which the Kundalini rises is not in the physical body, but in the subtle body (the subtle body is that in which the being goes out in deep trance or more radically, at the time of death); so also are all the centres. But as the subtle body penetrates and is interfused with the gross body, there is a certain correspondence between these chakras and certain centres in the physical proper. So figuratively we speak of the Purusha in this or that centre of the body. Owing to this correspondence, again, when the Ananda or anything else comes down into the being, it is the subtle body that it pervades, but it communicates itself through it to the gross body and its consciousness, so that it is felt as if pervading the body. But all that is very different from saying that the spirit is lodged in a gland. The gross body is an engine, a means of communication and action of the spirit upon the world and it is only a small part of the instrumentation. It is absurd to make so much of it as all that. It is a sort of false materialism intended to placate minds that have a scanty knowledge of Science. But what is the use of that? Everybody now knows 
that Science is not a statement of the truth of things, but only a language expressing a certain experience of objects, their structure, their mathematics, a coordinated and utilisable impression of their processes – it is nothing more. Matter itself is something (a formation of energy perhaps?) of which we know superficially the structure as it appears to our mind and senses and to certain examining instruments (about which it is now suspected that they largely determine their own results, Nature adapting its replies to the instrument used) but more than that no Scientist knows or can know.
Current publication:
Sri Aurobindo. Letters on Yoga // SABCL.- Volume 22. (≈ 28 vol. of CWSA).- Pondicherry: Sri Aurobindo Ashram, 1971.- 502 p.
Other publications:
1. 5695.
[A letter: ] Sri Aurobindo; Nirodbaran Nirodbaran Talukdar. Correspondence with Sri Aurobindo: The Complete Set [in 2 volumes].- 2nd ed., 3d inpression.- Volume 1.- Pondicherry: Sri Aurobindo Ashram, 2001.- 602 p.
2. 10233.
Sri Aurobindo. Letters on Yoga. I // CWSA.- Volume 28. (≈ 22 vol. of SABCL).- Pondicherry: Sri Aurobindo Ashram, 2012.- 590 p.