Accessory Organs

ACCESSORY ORGANS, such formations which, repeating the structure of one of the organs existing in the organism, are placed next to or at a certain distance from it and are usually of smaller sizes than the main ones. Accessory organs in the full sense, i.e., possessing all the attributes of the main ones, are rare. These include skeletal parts as organs of movement; accessory fingers (polydactyly), accessory mammary glands (polymastia), accessory spleens, thyroid glands, ovaries and testicles (polyorchism), teeth (polydentia), and the like are known. In the majority of cases, however, accessory organs are of a rudimentary character and are not represented by all the constituent parts proper to the main ones. These are so-called choristomas (Albrecht's choristomata). These include patches of the pancreas in the intestinal mucosa, sometimes without excretory ducts and without islands of Langerhans; choristomas from the tissue of the lungs, liver, and brain, placed in various regions of the organism, and the like (to be distinguished from dystopias!). After G. Driesch experimentally proved the possibility of the formation from a single fertilized egg cell of two or even several organisms complete in their form, the development of accessory organs exceeding the normal number in the organism cannot seem an inexplicable phenomenon. If each of the first two or four cleavage cells (blastomeres) of many animals is capable of reproducing a whole organism (totipotent), then subsequent cells in the order of multiplication, as they differentiate, only gradually lose this property and are cells capable of reproducing no longer all, but many parts of the organism (they are multipotent); finally, upon further multiplication, such cell aggregates are formed that are completely incapable of reproducing new forms; such are undoubtedly mature blood cells, erythrocaryocytes, giving rise to offspring only of their own kind (unipotent). Since organs for the most part consist of several different kinds of tissues, their formation is possible from totipotent and multipotent cell groups. The formative genesis of accessory organs has not been studied in detail, but there is reason to make certain assumptions. Thus, the narrowing of cell potency in the process of their multiplication occurs either gradually, with minimal changes, or by leaps, quickly leading the cells to the loss of potency. The first method makes it possible to preserve potency in time and increase the mass of a given cell aggregate. With a delay in rhythm, accompanied by minimal developmental changes, the formation of superfluous organs is possible, while doing no damage to neighboring areas of embryonic tissue that reproduce other organs. Causal moments in the change of the mechanics of organ development are still unknown. One can point with certainty only to the occasionally occurring manifestation of phylogenetic factors, as happens, for example, during the development of accessory mammary glands in humans, located in the order in which they are usual for other Mammalia (dogs). The possibility of the formation of accessory organs in the formed organism cannot be excluded if one takes into account the phenomena of so-called superregeneration, for example, the formation of two tails instead of one during regeneration in a newt. Metaplastic formation of accessory mammary glands from apocrine glands during lactation was traced by Seitz.