REPRODUCTIVE SYSTEM. 107 



maturity by the frequent modifications occurring in the ac- 

 companying conditions of life. Were no provision made for 

 these inevitable losses, species so propagating would be in 

 danger of extinction ; a result, however, ordinarily precluded 

 by the enormous number of eggs deposited at each sexual 

 period. It is estimated that at such times a single female 

 cod will discharge from 4,000,000 to 9,000,000 eggs, Doris, 

 600,000, and Gordius (hair-worm), 6,000,000. In Tcenia (tape- 

 worm), 200 eggs can be counted within each segment. 



Eggs are disposed of in various ways. In Fulgur (whelk) 

 they are contained within disks, composed of a hardened 

 secretion from oviduct, which are loosely connected longi- 

 tudinally. In Sepia (cuttlefish), each of the clustered egg- 

 capsules (marine grapes) contains from twenty to thirty ova. 

 The capsules of Doris assume the form of long lace-like 

 bands; those of Janthina that of a conoidal raft which remains 

 attached to parent; those of elasmobranchiate fishes, quad- 

 rate, tray-like figures with long, prehensile tendrils pendent 

 from angles. During development of eggs of oviparous 

 forms, they are either set entirely free and remain unpro- 

 tected, as in most aquatic animals, or are covered by the 

 female, as in the majority of birds. In the former case 

 they may be agglutinated in an albuminous product of the 

 oviduct, as in fresh-water Gasteropoda and Batrachia. In 

 osseous fishes they are often cast into grooves in the sand 

 (ridds). In Insecta they may be placed through ovipositors 

 in localities where, during the larval condition, the most ap- 

 propriate nourishment can be procured for the embryo, as in 

 Apis (bee), or where the larva can best procure its own food, 

 as in Cynips (gall-fly). 



Eggs are often carried by parent, viz.: in the marginal 

 pouches of discophorous Acalephse (jelly-fishes), between 

 the gills of Unio (mussel), within the peculiar shell of Ar* 

 gonauta (paper nautilus), to the sides of entomostracan 

 crustaceans, as Cyclops, or beneath the tail segments of 

 Homarus (lobster). They are at times secured to the skin 

 of abdomen, each by a separate pedicle, as in Aspredo icevis 



