FIELD T-2 

 Columns 58, 59, 60, and 61 



16. Symbol series 29--; process of change from one distinct juvenile form to another and 

 metamorphosis to the adult 



The development of individuals of some species involves one or more specialized juvenile forms, 

 each of which feeds and grows to its normal limits and is terminated by a morphological change, which 

 may be abrupt or may involve a quiescent stage of anatomical reorganization, to a more advanced stage 

 or the adult. The most remarkable of these are the developmental stages of arthropods, especially 

 insects, each stage terminated with a molt or a quiescent stage, ending with the final juvenile form 

 being graduated as the adult. The transition of aquatic juveniles of Amphibia to the truly amphibian 

 adult is another example. The symbol series, 29, is for these metamorphosing processes of individuals 

 from one developmental juvenile stage to the next. 



Certain other organisms reach an adult form only after a series of juvenile generations, a series 

 of which represent continually more advanced developmental stages to the adult generation. In the case 

 of plants and some lower animals (in particular, the Sporozoa, Cnidaria [Coelenterata], and Trematoda), 

 the product of sexual reproduction (the zygote) does not develop, as an individual, directly into an 

 adult, regarding the stage capable of sexual reproduction as the "adult" stage; instead, the zygote 

 develops into a wholly different type of individual whose structure and mode of existence frequently 

 differs radically from its parent and which reproduces asexually. (In some species, the offspring of 

 this asexual reproduction develops into still a third different type, also capable of reproducing only 

 asexually. Even more intermediate forms may occur in some species. ) While this asexually-reproducing 

 generation is so prominent in the life cycle of many organisms that it has resulted in the popular concept 

 of an "alternation of generations", the one or more asexually-reproducing generations of Sporozoa, 

 Cnidaria, Trematoda, and plants in general actually should be regarded as very elaborate juvenile forms. 

 In the case of the higher plants, this elaboration has reached such a level that the "adult" is reduced 

 to the most simple proportions, essentially remaining enclosed in the sporophyte (the asexually- 

 reproducing "juvenile" generation). These elementary facts are reviewed only to assist in drawing the 

 distinction between the point of change in form of a developing individual (e. g. , Insecta) and the point 

 of change of form when reproduction is involved in progressing from one developmental stage to the 

 succeeding stage (e. g. , Sporozoa, Trematoda, and plants). 



In the case of species having no "alternation of generations", the general process of develop- 

 ment of any individual, from zygote to adult, is coded by symbols of series 2A--, regardless of whether 

 its development involves one or more special juvenile transition processes coded by symbols of series 

 29--. The general final process of assuming adult characteristics by any individual is coded by 

 Symbol 2B, but when the test compound effect is expressed as being specifically on metamorphosis 

 processes which end with the adult insect or amphibian, Symbol 29 should be used. 



In the case of the species described above whose developments or life cycles involve a series 

 of juvenile generations (an alternation of generations), the general process of development of any 

 individual from the zygote to the mature asexually-reproducing stage typical of that particular generation 

 (i. e. , of that particular juvenile form), or of any individual from the bud, spore, or point of cell fission 

 to the mature form typical of that asexually-reproducing generation, or to the mature sexually-reproducing 

 "adult", is coded by symbols of series 2A--. The process which results in a new juvenile form of these 

 species or which results in the adult is not appropriate for association with items of the 29-- series, 

 but should be coded only as reproduction with a symbol of the A — series. 



17. Symbol series 3 ; coding of genetic changes which can be caused or affected or prevented 



by the test compound 



Aberrations of the genetic structures are coded by symbols of series 3 . Many of these are 



known to have a given incidence without influence of chemicals or any other specific agent. The test 

 compound's effect in causing or preventing the genetic change is indicated in Field T-l with Symbol 7 

 or 3, respectively. (Symbols 3, 31, 311, 312, 3121, 3122, 3123, 3124, 3125, and 34 all are coded 

 only with Symbol 7 or 3 [or 8, 9, A, or C], never with Symbol 1 or 2 of Field T-l. ) Symbols of the 

 312- series should not be used to code incidence of translocation, incidence of inversion, incidence 

 of gene mutation, etc. , as well as to code the process; this is the reason Symbols 1 and 2 of Field T-l 

 are not used with these symbols of Field T-2. The series could be expanded to include symbols specif- 

 ically for incidence of gene mutation, incidence of deletion, etc. , (i. e. , incidence of aberrations of 

 symbol series 31--) or for incidence of anatomical or physiological aberration coded by symbols of 



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