Fishes of the Western North Atlantic 521 



case that came under observation in an aquarium." It has been observed repeatedly that 

 the external openings of the oviducts are much swollen after an egg has been deposited, 

 as is the anal region in general with the margins of the pelvic fins. It has been suggested 

 that the deposition of one pair of eggs may soon be followed by the fertilization and 

 deposition of another pair, since maturing ova have been found in the ovary of females 

 in which the openings of the oviducts were still swollen. It appears that the egg cases, 

 when deposited, are either partly imbedded in the mud of the sea floor, whence they 

 are sometimes brought up in a dredge or trawl, or are attached to stones, etc. Develop- 

 ment in general resembles that of Sharks, the embryo temporarily having a cluster of 

 slender external gill filaments on either side.^^ Only a small part of the yolk is enclosed 

 in the embryonic yolk sac; the remainder breaks down to a creamy consistency, probably 

 to be absorbed by the embryo through the external gill filaments so long as these persist 

 and also to be taken in through the mouth. The period of incubation is between nine 

 and twelve months" in species for which information is at hand. When the young 

 hatch they already resemble their parents in all features that are diagnostic of the 

 order to which they belong. 



Habits. Chimaeroids, in breathing, take in water chiefly through the nostrils,^* 

 from which it passes through the grooves that connect the latter with the mouth (see 

 p. 517), which is kept closed for the most part. Respiration in Hydrolagus colUei of the 

 Pacific Coast of North America, the only species that seems to have been observed, 

 may be as rapid as 100 per minute.-' 



Chimaeroids are feeble swimmers, propelling themselves chiefly by undulations of 

 the posterior part of the body, second dorsal fin and caudal. The extensive pectorals are 

 described as being constantly in motion dorsoventrally, with undulations running from 

 the upper origin of the fin out around its rim.^" They serve as both propelling and 

 balancing organs. The pelvic fins are held horizontally and motionless most of the time, 

 and the claspers in males are pressed together in the midline behind the fins. When 

 motionless on the bottom, chimaeroids rest on the tips of the paired fins and on the tail, 

 and females are supported on the postanal ventral pad also, if they have this curious 

 structure (p. 523). They are more active by night than by day and are described as 

 avoiding strong light, at least under aquarium conditions. They are delicate fish also; 

 they struggle but little and soon die upon being taken out of water, nor do they make 

 any use of the dorsal spine as a weapon. But they can bite more sharply than one might 

 assume from the small size of the mouth. 



Their diet includes whatever small invertebrates and small fishes are available 

 locally, and those that occur in shoal water bite freely on almost any bait. 



25. Dean, Chimaeroid Fishes, Publ. Carneg. Instn., 32, 1906: 26, footnote. 



26. For illustrations of stages in embryonic development, see especially Schauinsland (Zoologica Leipzig, 16, 1903: 

 pis. 12-18 [Callorhinchus]); also Dean (Chimaeroid Fishes, Publ. Carneg. Instn., 32, 1906 [Hydrolagus]). 



27. Dean, Chimaeroid Fishes, Publ. Carneg. Instn., 32, 1906: 27; Whitley, Fish. Aust., i, 1940: 237. 



28. This is true of the Lungfishes (Dipnoi) also. 



29. Dean, Chimaeroid Fishes, Publ. Carneg. Instn., 32, 1906: 18. 



30. See Dean (Chimaeroid Fishes, Publ. Carneg. Instn., 32, 1906: 16-18) for an interesting eye-witness account of 

 their activities. 



