x SEGMENTATION 263 
The body of a King-crab can be analysed into twenty-one 
seements, but these do not all persist to the adult stage. They are 
grouped together in higher aggregates, or “ tagmata ” as Lankester 
calls them, and most of the segments bear paired appendages. 
The segments with their respective appendages and_ their 
grouping into tagmata are shown in the following scheme :— 
Appendages. 
, 1: Segment Median eyes Preoral 
lie an Rostrum He 
Te i Chelicerae a 
TVs ieee re Pedipalpi Lateral to mouth 
Ne 5 1st Walking Legs Postoral ~ Prosoma 
VI. . 2nd Walking Legs ee 
VER os 3rd Walking Legs 5 
VIII. a 4th Walking Legs Ae 
IX. ag Chilaria 5A 
xe a Genital operculum ab 
xele - Ist Gill-books 3 | 
XII. i 2nd Giill-books fa M 
XIII. 5, 3rd Gill-books Ae kaos ea 
XIV. Pe 4th Gill-books 55 | 
XV. ne 5th Gill-books Pe 
DOWIE 5 No appendages a 
XVII j ‘ ue | 
ae 2 Hp i Metasoma 
XX. 99 39 9? | 
XXI. ” ” 2 
We have followed Carpenter! in inserting the rostral segment. 
This corresponds with the segment that in Insects and Crustacea 
bears the antennae or first antennae respectively, the absence of 
these organs being one of the characteristic but negative features 
of all Arachnids. The evidence for the existence of this evanes- 
cent segment rests partly upon the observation of von Jawor- 
owski” on the vestigial feelers in an embryo Spider, 7vochosa, 
and perhaps more securely on the fact that, according to Korschelt 
and Heider, there is a distinct neuromere for this segment, 
between the proto-cerebral neuromere which supplies the eyes 
and the trito-cerebral neuromere which supplies the chelicerae. 
According to Brauer * the chelicerae of Scorpions are also supplied 
by the third neuromere. 
The bases of the chelicerae do not limit the mouth, but 
between and behind them is a ridge or tubercle which has the 
1 Quart. J. Micr. Sct. xlix., 1906, p. 469. 
2 Zool. Anz. xiv., 1891, pp. 164, 173. 
3 Zeitschr. wiss. Zool. lix., 1895, p. 351. 
