IOS BASHFORD DEAN. 



Obtain a Circulation of Water. This the capsule provides by 

 means of an elaborate system of perforations. These are bilat- 

 erally arranged, one series situated directly above the future gill 

 region of the embryo, and a second series in the sheath in which 

 the tail develops. These rows of perforations, moreover, are 

 graduated in size, suggesting that in certain regions the perfora- 

 tions are adapted to functional needs. The embryo causes a water 

 current to enter above the gills and to pass out on either side of 

 the tail. (Cf. the turning of the capsule against the current, like 

 a weather-vane.) In this connection the writer notes that he has 

 seen the embryo execute vigorously a rhythmic undulating move- 

 ment of its greatly elongated tail, which, provided with a con- 

 tinuous dorsal-caudal and anal-caudal fin, can only be interpreted 

 as a specialized organ for forcing the water backward through 

 the case. 



VIII. /// its Elaborate Provision for the Escape of the Embryo 

 at Term. - -By a delicate adjustment of the folded dorsal wall of 

 the capsule, a line of separation is formed in the respiratory per- 

 forations above the gill-region. Thus arises an opercular flap, 

 which finally opens in a way which suggests the opening of the 

 lamellar beak of a duck, and thus enables the young fish to 

 escape. This arrangement is a remarkably complicated one, the 

 valve being provided, among" other things, with roll-over margins 

 which preclude its being opened from without and so perfectly 

 adjusted that it opens only to the necessary degree. Once opened, 

 moreover, the valve margins cannot be restored in their former 

 relations, thus indicating that a state of tension has existed, com- 

 parable somewhat to that of dehiscent seed capsules. 



IX. In t/ie Progressive Changes in the Lifeless Substance of the 

 Capsule zvhich take place pari passn with the Developing Needs for 

 t/iese Changes on the Part of the Growing Embryo. - - At the time 

 the capsule is deposited it admits no water to its interior. In 

 fact, the unused tail sheath is then entirely filled with a plug of 

 thick albumen. The perforations are formed by a process of 

 weathering, during which delicate septa obstructing the openings 

 are gradually broken down and thus a greater current of water is 

 admitted to the interior of the capsule. In later stages these 

 openings are largest and most numerous. By the same process 



