* 
452 MB, W. K. PABKEB ON TEE SKELETON 
the Lamprey ; Tadpoles show rudiments of the intra-branchial arches of Sharks and 
Skates, By far the most generalised condition of the branchial skeleton is seen in 
the Tadpole of the Aglossal Dactylethra, and the cartilage of which it is composed 
is similar to that of the embryo Lamprey, 7 or 8 millims. in length. In that type and 
in the other Aglossal form, Pipa, the membranous space between the palato--quadrate 
arcade and the trabecula is almost absent. Yet in these, as in all the Anura, there 
is in the 1st visceral arch a cerato- branchial element, a free Meckelian (man¬ 
dibular) cartilage. Professor Huxley and I agree in thinking that we have found a 
true mandibular rudiment in the Lamprey after transformation ; certainly there is 
none in the Myxinoids ; and the quadrate region (and condyle) is quite suppressed 
in both the types of the Marsipobranchs (Myxinoids and Petromyzoids). More¬ 
over, the place where this tract should be, is not where we find it in the larval 
condition of the Frog or Toad, namely, at the fore part of the face; but under the 
exit of the 5th nerve, where we find it in transforming Tadpoles, whose tail has 
become a mere stump. 
This is easily accounted for ; in the Tadpole the small divided suctorial (lower 
labial) cartilage is carried by the mandibles—it is fixed between them ; these are its 
arms. During transformation, the lower lip of the Lamprey shoots forwards, and 
instead of lying back, as it did, under the hood-like upper lip, grows to the fore¬ 
front, and has the upper lip merely lying on the top of its upper rim in front; thus this 
production of the post-oral lip becomes the foremost part of the head. 
Hence anything corresponding to mandibles in the Lamprey are carried far away 
from their pier or “ suspensorium ; ” thus the hinge part of that pier is suppressed. 
The labials of the Lamprey correspond to the temporary labials of a Tadpole ; the 
cartilages that appear in that region (above), during transformation, correspond to 
what is seen in the upper fore-face of a Shark or Skate. 
The palato-quadrate arcade, with no quadrate lobe, and the distal cartilages 
attached to the suctorial disk, are all that can be accredited to the 1st visceral arch 
of the Lamprey. Its 2nd has no “ pharyngo-hyal ” element, but the lower part 
grows directly out of the back of the arrested suspensorium (part of the 1st arch); yet 
the lateral, sub-distal, and basal parts are well developed as the lingual skeleton. The 
only rudiment of an intra-hranchiaJ, behind the hyoid, is the hinder part of the large 
continuous basal bar (“lingual cartilage”); all the rest is extra-visceral, and after 
transformation the hyoid arch acquires an outer band of this nature. How the 
Myxinoids differ in these respects I have already shown, but their intra- visceral basket- 
work is dissociated from their branchial pouches, which are carried far back under the 
spine. Then, in their mouth, not circularly suctorial, as in the Lamprey, the dental 
armature, and its special buccal slceleton, is a huge development of parts, the like of 
which are feeble and subsidiary in the Lamprey. 
The Myxinoids do transform beyond the Ammocoetine stage, but they appear to have 
suffered some deflection during the process, and to have been stopped in their attempts 
