GASTEROPODES. 275 



pointed by Nature for introducing the young of animals to existence, 

 affording a noble field of observation to the speculative philosopher. 



A singular variety prevails among the different species of the tribe 

 wherewith we are now engaged one of the most prolific inhabiting the 

 waters of the deep. 



Probably the Tritonia Hombergii begins to breed at an early age, 

 and continues fertile very long. The presence of an ovarium and its 

 gradual advances, may be detected in many specimens through the 

 transparent skin of the under surface. 



Having attained maturity, the spawn is discharged as a rope from 

 the oviduct on the right side of the body. The parent affixes the end of 

 the rope to the solid substance whereon it rests, and gradually withdraws 

 during its further discharge. But its course being around the point of 

 fixture, the rope escaping forms a regular logarithmic curve, which, 

 from a peculiarity, is waved throughout the whole length. 



The spawn of smaller specimens is commonly of beautiful regularity, 

 consisting of four or six waving coils or volutes. 



But mark the provisions of Nature. In delivering itself of its pro- 

 geny, the parent must quit the original spot of fixture. If it did not re- 

 treat a mass of spawn would remain, but to preserve the whole entire 

 and undisturbed by its body, the second coil is apart from the first, and 

 the third from the second, hence an elegant figure from this mute mathe- 

 matician. 



Such is the result when the specimen is quite free and open ; and 

 sometimes a perfect form is produced. But such an extensive surface as 

 a larger specimen would require being generally interrupted or irregular, 

 corresponding irregularities disfigure the arrangement of the spawn. 

 Plate XXXIX. fig. 1. 



Thus the arrangement of the spawn from smaller specimens is more 

 definite. From whatever specimen it issues, however, the arrangement 

 peculiar to the species may be discovered. Nor does this belong exclu- 

 sively to Hornberg's Doris, for, as we shall see, it extends to others. 



The ovarium of the present species is very ample. Its progress is 

 exposed through the skin of the under surface, and from fainter indica- 



