28 



CHIM^ROID FISHES AND THEIR DEVELOPMENT. 



(plate n, fig. 5), if placed on a flat surface, it spreads out circu- 

 larly, measuring in this way over 5 cm. in diameter. It is pinkish 

 (it is earlier yellow, and later creamy white), although its tint 

 is probably due to the capillaries in the enveloping membrane. 

 These capillaries, it may be noted in passing, become focused 

 around a well-marked stigma. 



In the disposition of yolk the egg differs slightly from that of 

 typical selachians (e. g., as shown by Riickert in Torpedo). (Cf. 

 p. 47.) In the matter of fertilization, sperms have been found in 

 the uppermost portion of the oviduct, and there can be little ques- 

 tion that the earliest stages of fertilization here take place. It is 

 further evident that the eggs are received in the oviducts one after 

 another, for there is but a single funnel present, and it is prob- 

 able, from the condition of the ovaries examined, that the eggs 

 are shed from both right and left sides at almost the same time. 

 By this inference we can also best explain the passage of the 

 eggs, one to the right oviduct and one to the left, since if the first 

 egg were blocking the upper portion of one oviduct, the second 

 egg would naturally pass to the other. The fluidity of the egg 

 at this stage unquestionably aids it in passing through the narrow 

 opening of the oviduct in the zone of the capsular gland (plate n, 

 fig. 6), granting even that this opening is greatly enlarged at the 

 time of the egg's descent 



THE EGG-CAPSULE. 



The egg-capsules of Chimseroids* are illustrated in figs. 

 13-23, and a list of those hitherto described, together with notes 

 as to the depth at which they were collected, is given in Table C 

 on page 29. 



An examination of the capsules indicates that they may be 

 grouped according to the genera and species which they repre- 



Fig. 1 3. Spirangium (egg- 

 capsule of Chimaeroid?). 

 From lithographic stone 

 of Lerida (Spain). Ju- 

 rassic. After Sauvage. 



*In the instance of C. colliei, the parts of the young fish are found to have a definite relation to the egg-capsule, 

 and these relations are probably constant in other Chimaeroids. The capsule may therefore be referred to as containing 

 a case for the embryo, which is always subdivided into snout sheath, trunk sheath, and tail sheath. The case has 

 also a dorsal side, which bears anteriorly an opercular flap, which provides for the ultimate escape of the young, and 

 a ventral side, which is (usually) the more convex. Other descriptive terms are: Lateral zuebs, which are flanges of the 

 capsule extending outward from the case. These are sometimes strengthened transversely by stout undulating thick- 

 enings, rugfe, of the web; and these often pass over into, or are .associated with, more delicate and more numerous 

 distal rugulce, or both rugae and rugulae may become close-set, rib-like thickenings passing from case to web margin, 

 costie ; these terms will be found useful in description. Opercular ridges, overlapping, form together the rims of the 

 opercular flap. In their specialization these rims have sometimes protruding serrulcc, which interlock and form a close- 

 set grating, which admits water for the respiration of the embryo and which later breaks open to permit the young fish 

 to escape from the capsule. These grating-like fenestrulae are collectively homologous with the (pair or several pairs of) 

 lateral slits which appear near the rims of the egg-capsule of the shark or ray. Continuing the line of the fenestrulae, 

 ventilating apertures are also present at the sides of the tail-sheath, and these may be termed caudal fores. They are 

 typically furnished with "tongue-bars," which double the number of simple openings. A dorsal keel is present in the 

 capsules of Chimaera. 



