XVI CYCLOSTOMATA 429 
tinuous. A gall-bladder is present, and also a bile duct open- 
ing into the gut. In its mode of life, and especially in the 
manner in which it obtains its food, Ammocoetes presents a 
most remarkable resemblance to Amphiovus and the Ascidians. 
In the median line of the pharyngeal floor there is an open 
groove, the hypopharyngeal groove or endostyle, and a tract of 
ciliated cells along the dorsal wall represents a hyperpharyngeal 
groove: connecting the two in front there is a peripharyngeal 
cilated groove." The Ammocoetes feeds on small food particles 
carried through the mouth into the pharynx by currents of 
water produced by ciliary action. The food becomes entangled 
in strings of mucus probably secreted by the cells lining the 
endostylar groove. The mucus is then swept upwards ingthe 
pharyngeal groove, and finally wafted backwards to the stomach 
and intestine by the cilia of the hyperpharyngeal band. The 
skin exhibits the remarkable peculiarity of containing a peptic 
ferment capable of digesting proteids in a ‘2 per cent solution 
of hydrochloric acid. As the larva lives buried in the mud, the 
epidermic secretion probably helps to keep the skin free from 
bacteria, microscopic spores, and fungoid, or other parasitic 
growths.” The young Lamprey lives as an Ammocoetes from 3-4 
years, and then in the course of a few weeks in the winter it under- 
goes a metamorphosis, losing its larval characters and acquiring the 
structure and habits of the adult. During this period the buccal 
funnel is completed and teeth are developed. The eyes approach 
the surface and become functional. The continuity of the median 
fins becomes interrupted. The endostylar groove becomes trans- 
formed into a thyroid gland, the gall-bladder disappears, and the 
bile duct becomes obliterated and changed into a mass of small 
follicles. The skull and branchial basket complete their develop- 
ment. At the same time the pharynx loses its connection with the 
rest of the alimentary canal and remains as the branchial canal. 
The so-called oesophagus of the adult is apparently a new formation 
which grows forwards and acquires a connection with the mouth. 
It is probable that it represents a hyperpharyngeal groove con- 
stricted off from the dorsal wall of the pharynx. 
Both the marine Lamprey and the “ Lampern’ 
? 
are captured 
1 Dohrn, Mitth. Zool. Stat. Neapel, vi. 1886, p. 59; Shipley, Quart. Journ. 
Microsc. Sci. xxvii. 1887, p. 325. 
2 R. Alcock, Journ. Anat. and Phys. xiii. (N.S.), 1899, p. 623. 
