1912.| R. B. SEYMOUR-SEWELL : Surface-Living Copepoda. 317 
ing with a new species ; but on measuring these examples and plot- 
ting the results obtained with those of the undoubted examples 
of L. euchaeta, I found that they formed a mathematically exact 
continuation of the series. As, in addition, these examples have 
only been obtained in association with large numbers of L. euchaeta, 
and a prolonged search has failed to reveal any immature 
forms other than those of L. ewchaeta that could correspond with 
this type, I have come to the conclusion that we have here in the 
Copepoda an exactly similar state of affairs to that which has 
been shown by Fowler to exist among the Ostracoda (Halocypridae). 
The actual measurements of all the examples in each group are 
shown in text-figure I. 
It is at once evident that the different measurements fall into 
a series of groups, each having a normal curve of variation, and 
although the extremes of variation of successive groups may to 
some extent overlap yet each shows a very definite mean. 
Taking first the growth stages of the female, the mean length 
measurement at each successive moult is given below and for pur- 
poses of comparison I have also given the lengths calculated from 
the smallest stage by multiplying each stage by the growth- 
factor. 
| 
Observed size. Calculated size. | Growth-factor. 
|_——— =) 
mm. | mm. | 
Stage 6 oe - + | 0'593 | 0593 | I°4 
ae 5 se 20 | 0°844 | 0°830 | 1°4 
4 ats sl 1°168 | 1162 | 1°4 
mas Br Peel 1°620 O27 | 1°27 
qe a ye 2°054 2066 | OG) 
Meet ics 56 2'639 | 2°624 | 
From the above it would appear that during the early 
moults the growth-factor is 1'4, whereasin the last two moults this 
factor falls to 1°27. 
This drop in the factor is of some interest inasmuch as it 
has not been found to exist in the Ostracoda, though it un- 
doubtedly is a feature in the growth stages of some of the higher 
Crustacea. 
Turning now to the consideration of the males I found that, 
previous to stage 4, it was quite impossible to differentiate be- 
tween the two sexes, and hence the growth moults can only be 
studied from that point. 
The mean length-measurements of the various stages of the 
male are as follows, and here again I have given the calculated 
measurement for comparison. 
