W. E. Agar 185 



produced by these conditions, but in the main part of the line, under 

 the normal conditions, "degenerates" have been extremely rare. 



On two occasions however there was an epidemic of deaths among 

 young individuals and embryos in the part of the line under normal 

 conditions. The first of these occurred in generation 4, the second in 

 generation 30. The second one was very instructive as at that time 

 I had under identical conditions parallel cultures of two other lines 

 started from specimens obtained from different localities to that from 

 which the parent of the principal line was obtained. The two lines in 

 question were started from parthenogenetic females from Cambridge 

 and Beith respectively, and generation 13 of the Cambridge line and 

 generation 14 of the Beith line were contemporary with generation 30 

 of the main line, and all of them showed simultaneously the same 

 "degeneration." In the main line four females laid altogether 19 eggs, 

 from which only two living young were obtained. In the Cambridge 

 line, six females laid together 31 eggs, and only 12 living young were 

 born, while from the Beith line no living young were produced from 

 29 eggs laid by six females. These figures all refer to the first broods 

 of the parents. All three lines had completely recovered by the second 

 broods of the same generation, the second batches of eggs laid by all 

 these sixteen females developing perfectly normally into normal healthy 

 young. Moreover, except for occasional cases here and there, no more 

 " degenerate forms " appeared in any of the three lines. In fact in the 

 main line (Table I), in the last eleven generations not a single one of 

 the new-born young isolated failed to arrive at maturity, and to produce 

 perfectly normal young. Clearly therefore the temporary and simul- 

 taneous disturbance in the three lines was due to some temporary 

 unfavourable factor in the environment, although there was no reason 

 to suppose that the water in the Lepidosiren tank varied in any 

 way from the normal at that time ; while all the other factors of the 

 environment were, so far as could be ascertained, unaltered. 



The last of the visible accompaniments of degeneracy observed by 

 Papanicolau which we need consider is the diminution in number and 

 the increase in size of the parthenogenetic eggs as the line grew older. 

 These are really largely the same phenomenon, there being a strong 

 organic correlation between the number and size of the eggs, the larger 

 the number the smaller being their size. This is the case, that is to 

 say, if we judge the size of the eggs by that of the new-bom young 

 hatched fi-om them. I have found it very difficult to get a satisfactory 

 series of measurements of the eggs owing to their rapid increase in size 



