VARIATIONS BETWEEN CHAPTERS
Each organ serves a specific function as outlined above. Although a Chapter's Apothecaries and surgeons are able to perform the necessary implant operations, they do not necessarily understand the exact functioning of each organ. The processes involved are incredibly ancient. Procedures are handed down from generation to generation, becoming increasingly ritualised and misinterpreted. For these reasons, the efficiency of each organ differs from Chapter to Chapter, depending on the condition of that Chapter's gene-seeds and the degree of debasement of its surgical procedures. In some Chapters, mutation of gene-seed, poor surgical procedure, or inadequate post-operative conditioning, has twisted the functioning of implants. For example, the omophagea gene-seed of the Blood Drinkers has mutated so that all Blood Drinkers have an unnatural craving for blood. In other Chapters individual organs are either useless or absent altogether.

REPRODUCING ZYGOTES
Gene-seed can only be obtained by removing one or both progenoid organs from a living (or very recently deceased) Marine. For this purpose, Space Marine Apothecaries carry a special device known as a reductor, which they can use in battlefield conditions to remove the progenoid glands of a fallen
Marine. The whole purpose of the progenoid organ is to provide gene-seed to enable the Chapter to continue. It is not possible to create a zygote in any other way. Each Chapter's stock of gene-seed is therefore unique to itself. Gene-seed has a great deal of religious significance to a Chapter, representing its identity and future. Without gene-seed, a Chapter has no future. The extinction of a type of gene-seed means that a zygote has been lost forever. The extinction of a Phase 18 or 19 gene-seed would effectively mean an end to a Chapter.

As each Marine has only two progenoid glands, the rate at which a Chapter can create new Marines is restricted. It may take many years for a Chapter to rebuild itself after heavy losses. Gene-seed is often rendered useless if a Marine is exposed to high radiation levels or other forms of genetic disturbance. The efficiency of different Chapters' progenoid gene-seed also varies, so some Chapters are able to make up their numbers faster than others.

A new Chapter cannot be founded overnight. A single suitable gene-seed must be selected for each zygote. Zygotes are then grown in cultures and implanted into human test-slaves. These test-slaves must be biologically compatible and free from mutation. Test-slaves spend their entire lives bound in static experimental capsules. Although conscious, they are completely immobile, serving as little more than mediums within which the various zygotes can develop. From the original slave come two progenoids, which are implanted within two more slaves, from which come four progenoids and so on. It takes about 55 years of constant reproduction to produce 1,000 healthy sets of organs. These must be officially sanctioned by the Master of Adeptus Mechanicus and then by the High Lords of Terra speaking for the Emperor. Only the Emperor can give permission for the creation of a new Chapter.

RECRUITMENT AND INITIATION
The various implants cause vital changes in a Marine's physique and mental state. Many of these changes are controlled by natural hormonal secretions and growth patterns. Implants may not prove effective, or may not become fully functional, if they are carried out once the recipient has reached certain stages of natural development. It is therefore inevitable that recruits must be reasonably young. Tissue compatibility is also essential, otherwise organs may fail to develop properly.

The third consideration is mental suitability. The catalepsean node, occulobe, and sus-an membrane will only develop to a useable condition under the stimulus of hypnotic-suggestion. A recruit must therefore be susceptible to this particular treatment.

These considerations mean that only a small proportion of people can become Space Marines. They must be male because zygotes are keyed to male hormones and tissue types, hence the need for tissue compatibility tests and psychological screening. If these tests prove successful, a candidate becomes a neophyte. With the completion of organ implantation and attendant chemical and hypnotic training, the subject becomes an initiate. An initiate receives training before joining the ranks as a full brother. A Marine usually joins the ranks between the ages of 16-18, but such are the hormonal changes induced by the process of creating a Space Marine that recruits are physically fully grown before then. Pressures during wartime may accelerate the process.