C YC LOS TO MI : CEPHALOCHORDA . 43 7 



brata. They eat their way into the coelome of other Fish, e. g. Cod, 

 Sturgeon, &c. The Lampreys attach themselves to Fish by the suctorial 

 mouth, and scrape their flesh away with the teeth of their tongue. 



The Cyclostomi are divided into two Orders as follows : 



1. Hyperoartia. Dorsal fin well developed ; nasal passage closed. One family, 

 Petromyzontidae, the Lampreys, both marine and fluviatile, with several genera 

 found in various parts of the world ; Petromyzon, in Europe, America, Japan, and 

 West Africa ; Mordacia, in Tasmania and Chili ; Geotria, in South Australia and 

 Chili ; Ichthyomyzon, west coast of North America. 



2. Hyperotreti. Dorsal fin feebly developed ; nasal passage opening into the 

 pharynx. One family, Myxinoidei, containing two genera, Myxine, the Hag-fish, 

 from the northern seas and Pacific coasts of temperate South America; and 

 Bdellostoma, from the southern seas (Cape of Good Hope, New Zealand, coasts of 

 Chili). Exclusively marine. 



Anatomy ofPetromyzon Planeri, Langerhans, Untersuchungen uber P. Planeri, 

 Freiburg, 1873. Metamorphosis, &c., Schneider Beitrage zur Vergleich. Anat. &c., 

 der Wirbelthiere, Berlin, 1879. Development, Balfour, Comparative Embryology, 

 ii. 1 88 1 ; of visceral arches, Dohrn, Mitth. Zool. Stat. Naples, v. 1884. Myxinoidei. 

 Vergleich. Anat. des Myxinoiden, J. Miiller, Berlin, 1835-40-41; cf. Abhandl. 

 Akad. Berlin, Classis Phyica. 1834, 365-38, 39. Epidermis of Petromyzon, Foett- 

 inger, Bull. Acad. Roy. Belg. (2) 41. 1876,- summary of do., and on Myxine, Blom- 

 field, Q. J. M. xxii. 1882. 



Cranium, W. K. Parker, Ph. Tr. 174. 1883; cf. Huxley, Journal of Anat. and 

 Physiol. x. 1876. Skeletal tissue, Gegenbaur, J. Z. v. 1870. Head Muscles, Fiir- 

 bringer, J. Z. ix. 1875. 



Brain in Ammocoetes and Petromyzon Planeri, Wiedersheim, J. Z. xiv. 1880; 

 in Petromyzon, Ahlborn, Z. W. Z. xxxix. 1883. 



Cranial nerves of Petromyzon, Ahlborn, Z. W. Z. xl. 1884. Spinal and visceral 

 nerves of Cyclostomi, Ransom and D'Arcy Thomson, Z. A. ix. 1886. 



Pronephros of Myxine, Weldon, Q: J. M. xxiv. 1884; sexual products, Cun- 

 ningham, Q. J. M. xxvii. (i), 1886. Urogenital system of Cyclostomi, W. Miiller, 

 J. Z. ix. 1875. 



Abdominal pores and urogenital sinus, Ewart, Journal of Anat. and Physiol. 

 x. 1876. 



SUB-PHYLUM AND CLASS CEPHALOCHORDA. 

 (A crania ; Pharyngobranchii\ 



Marine Chordata, with a body pointed at each end, and provided with a 

 continuous dorsal, anal, and caudal ctiticular fin. There are no paired limbs : 

 no skull, vertebral arches and centra : no jaw-arches : no differentiated brain, 

 sympathetic nervous system, or auditory organ : no heart, spleen, kidneys, or 

 sexual ducts. There is but one genus contained in the group Amphioxus 

 with species found near the coasts in various parts of the world. The animal, 

 when adult, lives buried in sand with the oral aperture just exposed. 



