The segments with their respective appendages and their grouping into tagmata are shown in the following scheme:— Appendages. I. Segment │Median eyes │Preoral │Prosoma II. „ │Rostrum │ „ │ „ III. „ │Chelicerae │ „ │ „ IV. „ │Pedipalpi │Lateral to │ „ │ │ mouth │ V. „ │1st Walking │Postoral │ „ │ Legs │ │ VI. „ │2nd Walking │ „ │ „ │ Legs │ │ VII. „ │3rd Walking │ „ │ „ │ Legs │ │ VIII. „ │4th Walking │ „ │ „ │ Legs │ │ IX. „ │Chilaria │ „ │ „ X. „ │Genital │ „ │Mesosoma │ operculum │ │ XI. „ │1st Gill-books │ „ │ „ XII. „ │2nd Gill-books │ „ │ „ XIII. „ │3rd Gill-books │ „ │ „ XIV. „ │4th Gill-books │ „ │ „ XV. „ │5th Gill-books │ „ │ „ XVI. „ │No appendages │ „ │Metasoma XVII. „ │ „ │ „ │ „ XVIII. „ │ „ │ „ │ „ XIX. „ │ „ │ „ │ „ XX. „ │ „ │ „ │ „ XXI. „ │ „ │ „ │ „ We have followed Carpenter[210] 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 evanescent segment rests partly upon the observation of von Jaworowski[211] on the vestigial feelers in an embryo Spider, _Trochosa_, 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[212] the chelicerae of Scorpions are also supplied by the third neuromere.