EEPORT ON THE STOMATOPODA. 
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frustrates the attempt to trace the gradual growth and metamorphosis of the larvae in 
this way, and there is no other resource except comparison. 
The first step in this direction is to trace the history of each larval type, by the 
selection and comparison of those larva which belong to the same series. In accomplish- 
ing this I have been guided in part by general resemblances, but more especially by 
comparative measurements. After I had tabulated the measurements in millimetres of a 
number of specimens, which resembled each other quite closely, and formed a tolerably 
complete series, I failed at first to trace through the columns of the table any such 
conformity to a general law as I had expected, but more careful examination indicated 
that this might be due to the fact that the history of the larva consists of metamorphosis 
as well as growth, and that the size of one organ might, when compared with that of 
another organ, show a gradual decrease during the successive stages, while its absolute 
size was actually increasing. I therefore reduced all my measurements to a common 
standard, and expressed them in thousandth parts of the total length of the larva at 
each stage instead of in millimetres, and I found that this at once introduced order 
where all had before been confused, and that, when thus reduced, the measurements 
usually enabled me to decide with confidence whether a given larva does or does not 
belong to a certain series. 
In a few cases these comparative measurements gave proofs of specific identity which 
could hardly be made more conclusive by rearing the larvae. Thus the lengths of the 
series of Coronis larvae shown in PI. XIII. figs. 1-8 are as follows, and if the length of the 
first stage be successively multiplied by five-fourths of itself, and this number by five- 
fourths of itself again, and so on, we obtain the series of numbers given in the second line, 
and as it is not conceivable that an accidental collection of larvae should exhibit such 
exact conformity to a numerical law, we may feel certain that these larvae are genetically 
related, that they belong to one species or else to closely related species, and that the 
series is consecutive, with the exception of one missing stage before the last. 
4T6 mm. 
5 - 29 mm. 
6 - 49 mm. 
10'21 mm. 
4-16 „ 
5-20 „ 
6-50 „ 
8T3 mm. 
10T6 „ 
After one or two series had been traced out in this way, the general character of the 
metamorphosis itself became a trustworthy guide for establishing the series for a closely 
related species, and thus simplified the labour, and the next step was the reference of 
each larval type to its proper adult genus. 
If the differences between the larvse are due to secondary modification, we should not 
expect the larvse of two distinct adults to become modified in the same way, and 
although it is of course possible that the larvse of two closely related adults might 
