THE ENTEROPNEUSTA. 663 
growth of the animal. This latter condition precludes the direct use of absolute measurements. 
It is obvious that a ratio must be made use of—a simple ratio whose two factors are 
equally affected by growth changes. Though several distinct regions may be distinguished 
in the body of a Ptychodera, with the exception of the collar and branchial region, their 
limits are not very clearly defined. Accordingly most attention has been paid to the ratio 
of branchial to collar length. And this more especially since any collection of Enteropneusts 
will be largely made up of damaged specimens, and though few specimens may attain to 
anything like completeness, yet in the great majority both collar and branchial regions will 
be perfect. Great accuracy in the measurement of such animals as the Enteropneusta is 
out of the question since in a soft-bodied creature relative differences in’ the state of 
contraction of the various body regions may easily occur, whilst the personal equation must 
enter largely into the result. In the present instance however all the material had been 
treated in the same way, ze. had been narcotised in chloral hydrate for several hours before 
preservation, thus ensuring an equable contraction, whilst the personal equation was as far 
as possible eliminated by my making all the measurements within the space of a week or so. 
By far the most frequent of the varieties described in this paper is laccadivensis, and 
it is here that the measurements are most complete. In addition to the length of the 
collar and of the branchial region the total length and the length of the genito-hepatic 
regions was measured wherever the specimen was sufficiently perfect. The width of the 
collar was also registered. The results for 123 specimens (fewer in the case of the genito- 
hepatic and total lengths) are given in Table 11, pp. 671—2, and in the diagram on p. 666. 
Before however any value can be attached to these figures it must be shewn how, if at 
all, growth affects these ratios. 
The method employed for estimating growth changes was to divide the animals into 
several groups according to size, and to calculate the above three ratios for each group 
separately. As the collar width was sometimes less, sometimes greater, than the length it 
was thought advisable to take this factor also into account, and in the case of laccadivensis 
the following groups were made. 
Numbers in Group 
Branchial Genito-hepatic Total 
Group 1. Collar length x breadth not >16 ............... 47 38 19 
m 2b aS ty) PRS > 16, but not > 25... 45 33 17 
5 Ok ”» » ” SP, sy py Se blshes 27 15 13 
sree * fie oe of Sev eciea atic aa eeicichis ebesinie= 4 —- _- 
123 86 49 
The mean of each ratio was then caleulated for each of the above groups with the 
following result :— 
No. of Specimens 
Branchial length 
settee ee Ne 0 = 2°08 47 
Colle Iocan Mean for Group 1 0: 7 
” ” ” 2 = 218 45 
” ” ” 3 = 2°36 27 
4=277 4 

Average 2°20 
