556 PISCES FISHES. 



adherent earth externally, with moist slime internally, and with a lid, 

 on which there is always a small aperture. Thus encapsuled, the 

 animal may remain dormant for many months, e.g. from August to 

 December. The air seems to pass directly from the mouth of the 

 burrow, through the aperture of the capsule-lid (which is produced 

 inwards in a short pipe) to the external nostrils, and thence to the 

 lungs. The nourishment appears to be derived from a store of fat 

 deposited in the lymphoid tissue around the reproductive organs and 

 kidneys, and among the lateral muscles of the tail (cf. fatty bodies in 

 caterpillars, amphibians, etc.). Moreover, some of the muscles are 

 replaced by fat, and others undergo a pathological granular degenera- 

 tion (cf. lamprey). To a certain extent, therefore, the dormant 

 animal lives on its own tail. It is probable that leucocytes aid in the 

 absorption and transportation of the degenerated muscles (cf. tadpoles). 

 These capsules, with the surrounding earth, have often been transported 

 from Africa to northern Europe, without injury to the dormant fish 

 within. 



A few of the anatomical characteristics of Protoptents may now be 

 noted, following Professor W. N. Parker. 



The paired fins are filamentous, and seem degenerate when compared 

 with those of Ceratodiis, having only a few reduced lateral rays on the 

 segmented axis. The tail is symmetrical, and ends in a filament, 

 which, like the end of the fins, is often bitten off; both tail and fins 

 may be regenerated after serious injuries. 



In the skin are very numerous mucus-secreting goblet cells, and there 

 are also (especially on the snout) multicellular glands, which are absent 

 from most fishes, though common in Amphibians, Reptiles, and 

 Mammals. There is a continuous lateral line. 



There is a spiral valve in the large intestine ; the cloaca has an 

 associated " caecum " ; the pancreas surrounds the bile-duct, and, though 

 large, is almost hidden within the walls of the gut ; the spleen is also 

 large, but inconspicuous. Cilia are present throughout the stomach and 

 intestine, and there are no differentiated gastric or intestinal glands. 



Behind the hyoid are five rudimentary branchial arches. There are 

 five gill-clefts, covered by an operculum, outside which are three 

 external epidermic gills. 



The lungs are paired along almost their entire length, and extend 

 under the notochord to the end of the body cavity. Although the lungs 

 lie dorsally, they probably arise as a ventral diverticulum, as in higher 

 animals. 



The blood is remarkable for the large size of its elements, and for the 

 predominance of white over red corpuscles. In general structure the 

 heart is like that of Ceratodus. There is but one auricle, but a dorsal 

 fibrous ridge hints at its division. The conus arteriosus has a long 

 spiral longitudinal valve, and minute pocket-like valves. From the 

 conus four branchial arteries arise on each side, and pass to the first four 

 branchial arches, and the effect of the longitudinal valve is that the 

 anterior pair contain blood already purified in the lungs ; the posterior 

 pair carry almost unmixed venous blood. The efferent branchials unite 

 in a transverse trunk, and then form the dorsal aorta ; and from the 

 root of the aorta a paired pulmonary artery arises, the left supplying the 



