At transformation these muscles proliferate and develop enormously, and form the bulk of the large basilar muscle which {308}surrounds the throat ventrally and laterally, and is the most bulky muscle in the suctorial apparatus. The velar or mandibular nerve supplies in Ammocoetes the muscles of the lower lip. In Petromyzon it supplies also the longitudinal muscles of the tongue. The tongue-cartilage first develops in the region of the median ventral tentacle, and there the longitudinal tongue-muscles first begin to develop, not from the rudimentary muscles in the tongue but from those in the lower lip region. In Ammocoetes the tentacular nerve supplies the rudimentary muscles in the tentacles and the muscles of the upper lip. The latter disappear entirely at transformation, and in Petromyzon the tentacular nerve supplies the circular, pharyngeal, and annular muscles, which are derived from the rudimentary tentacular muscles. For the convenience of my reader I append here a table showing my conception of the manner in which the endognathal and ectognathal segments of the Palæostracan are represented in Ammocoetes. It shows well the uniform manner in which all the individual segmental factors have been fused together to represent the appearance of a single segment (van Wijhe's first segment) in the case of the four endognathal segments, but have retained their individuality in the case of the ectognathal segment. +----------+----------+---------------------------+----------+----------+ | | | Appendages. | | | |V. Wijhe's|Eurypterid+-------------+-------------+ Appendage| Skeletal | |segments. |segments. | Eurypterid. | Ammocoetes. | nerves. | elements.| | | | | | | | +----------+----------+-------------+-------------+----------+----------+ | | | | | | | | | 2} | | | 1 | 1 | | 1 | 3} | 4 | 4 |Tentacular|Tentacular| | | 4} | Endognaths | Tentacles | to 4 | bar to 4 | | | 5} | | | tentacles| tentacles| | | | | | | | +----------+----------+-------------+-------------+----------+----------+ | | | | | | | | 2 | 6 | 1 | 1 | 1 Tongue | 1 Tongue | | | | Ectognath | Tongue | nerve | bar | | | | | | | | +----------+----------+-------------+-------------+----------+----------+