By means of an appropriate mathematical model (Sager's 2-components-concept) a delayed spontaneous pubertal growth spurt can be demonstrated in girls with 45,X Ullrich-Turner syndrome (UTS) (n1 = 45) as well as in those with 45,X/46,XX mosaicism (n2 = 14) never treated with any growth stimulating drug. On the average, this growth spurt begins later and its extent is smaller (mean growth rate = 3.10 and 2.79 cm, respectively, in the 15th year of chronological age) than in normal girls. The delay in acute growth spurt corresponds very well to the delay of skeletal maturation in the UTS (on the average 2 to 3 years of chronological age).

Figure 1. Visually gained growth curves have been added for single specimens that leave some doubt as to the existence of an inflexion point. I n this paper a cross-sectional evaluation of growth behaviour is carried out with nine funtions using nonlinear regressions. Five growth functions yield almost equally good results with a final valve height just below 100 mm. An inflexion point is either present in early youth or lacking altogether, depending on the growth function used.

Former investigations into the age structure of Brunchiostorna lanceolaturn by COURTNEY (1975) and GOSSELCK and SPITTLER (1979) centered on the assumption that the relative length growth of this species diminishes logarithmically with increasing age. Regarded from a mathematical point of view, this relation demands an exactly channelled form of growth, and this can be checked by submitting the basic values t o nonlinear regression. As the results of this procedure yield considerable deviations from the measured data, the function of length growth given by PUTTER and v. BERTALANFFY is applied and reduces the error by about 70 a, ' , , . As a consequence the former assumption must be corrected.

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