104 



SEVENTH REPORT. 



5. Length of the carpopodite of the first walking leg of the right side; measurements from the same 

 points as in 4. 



6. Length of the carpopodite of the second walking leg of the right side; measurements from the 

 same points as in 4 and 5. 



7. Length of the propodite of the great cheliped of the right side from the proximal dorsal process 

 where it articulates with the carpopodite to the extreme distal end. Fig. I. f-g. 



8. liCngth of the propodite of the second walking leg of the right side; measurements from the same 

 points as in 7. 



9. Length of the propodite of the second walking leg of the right side; measurements from the same 

 points as in 7 and 8. 



10. Length of the carapace from the tip of the ro.struni to the posterior edge on dorsal median line. 

 11 Breadth of the head between points on either side in the .cervical groove just in front of the 



two lateral spines. 



FIG. I. 



Figure of portion of great cheliped showing points from which measurements were taken. 

 M. — Meripodite. C. — Carpopodite. P. — Propodite. 



All the measurements were made with a pair of fine pointed dividers, and read off by 

 means of a hand-lens on a millemeter rule graduated to fifths of a millemetre. By noting 

 whether the points rested on or between marks the measurements could be made to tenths 

 of a millemetre. They may be considered to be accurate to a fifth of a millemetre. 



For the eleven characters measured the means, standard deviations and coefficients 

 of variation together with their probable errors were determined. The coefficients of 

 correlation and their probable errors were computed for all possible pairs of the char- 

 acters. There are with eleven characters fifty-five different combinations of two possible. 



We may turn now to the results. In Table I are given the values of the coefficients of 

 correlation between homologous joints on the one hand, and non-homologous joints on 

 the other. 



TABLE I. 



Correlation Between Joints of Crayfish Appendages. 



A. HOMOLOGOUS JOINTS. 



Joints. 



Meripodite-meripodite. . . 

 Carpopodite-carpopodite 

 Propodite-propodite .... 

 Mean 



Legs I— IL 



.9665+ .0026 

 .9034± .0074 

 .9506± .0039 

 .9402+ .0104 



Legs II— III. 



.9729+ .0021 

 .8854+ .0087 

 .9678+ .0025 

 .9420+ .0156 



Legs I— III. 



.9686+ .0025 

 .8685+ .0099 

 .9468+ .0042 

 .9280+ .0167 



B. NON-HOMOLOGOUS JOINTS. 



Joints. 



Meripodite-carpopodite . 

 Carpopodite-meripodite 

 Carpopodite-propodite . 

 Propodite-carpopodite . 

 Meripodite-propodite. . . 

 Propodite-meripodite. . 

 Mean 



Legs I— II. 



.8908+ .0083 

 . 9502 + . 0039 

 .9531 ± .0037 

 .8898 + .0084 

 .9578+ .0033 

 .9440+ .0044 

 .9309+ .0080 



Legs II— III. 



.8632+ .0102 

 .9185+ .0063 



.9056 + 

 . 8673 + 

 .9626 + 

 . 9670 + 

 .9140 + 



.0072 

 .0099 

 .0030 

 .0026 

 .0119 



Legs I— III. 



.8652+ .0101 

 .9601+ .0031 

 . 9530 + . 0037 

 .8613 ± .0104 

 .9646± .0028 

 .9539+ .0036 

 .9264+ .0123 



In this table and tho.se following the numerals I, II and III refer to the great cheliped, first and second 

 walking legs respectively. In each case the name to the left in the column marked joints goes with 

 the numeral to the left under Legs, and the right with the right. Thus under B. the .8908 in the col- 

 umn headed Legs I — II and in the row marked Meripodite-corpopodite is the co-efficient of correla- 

 tion between the meripodite of the I leg and the corpopodite of tlie II leg. 



Comparing mean coefficient' for homologous joints and nOn-homologous joints we have 

 the following results: 



