588 THE POPULAR SCIENCE MONTHLY. 



an opening to tlie exterior is formed. The central space now be- 

 comes the stomacii, d, in Figs. 4 and 5, and the opening becomes 

 the month, e, in Figs. 4 and 5. Soon after the mouth is formed a 

 circlet of tentacles is developed around it, and the larva becomes 

 a hydra, but a hydra adapted to a floating life rather than a fixed 

 life, as shown in Fig. G. 



It is now able to capture and digest food and to lead an inde- 

 pendent life, and it grows rapidly, although it has as yet no loco- 

 motor organs, and drifts at the mercy of the waves. 



Soon the stomach becomes flattened and the mouth pushes in 

 toward the center of the sphere, carrying with it the surface layer 

 of cells, and thus giving rise to a concave, hollow bell-cavity open- 

 ing to the exterior, as shown in Fig. 7, in which d is the flattened 

 stomach, e the mouth, and / the cavity of the swim-ball. 



As the mouth is pushed in, the tentacles are left behind and 

 remain on the edge of the bell in the position which they occupy 

 in the adult. The animal grows rapidly, the tentacles lengthen, 

 and, after some slight changes which do not now concern us, the 

 larva becomes converted into an adult, like the one shown in Fig. 

 2, and again reproduces its kind by fertilized eggs. 



The life-history of Liriope is simple and direct. There is a 

 metamorphosis, and the animal passes through a planula stage, a 

 hydra stage, and a medusa stage ; but its identity is never lost, 

 and the larva is the same individual as the adult, as is shown in 

 the following diagram : 



II. LiRioPE. — E^ = Planula = free Hydra = Medusa < eggs. 



Although most of the text-books state that the direct history 

 of Liriope has been produced by the gradual simplification of a 

 complicated life-history like that of Dysmorphosa, there is no evi- 

 dence whatever that this is the case, and the fact that the develop- 

 ment of Liriope resembles that of all ordinary animals is in itself 

 an indication that its simplicity is not secondary but primitive. 

 This view is rendered still more certain by the study of other 

 jelly-fishes which exhibit successive steps in the process of com- 

 plication. 



De. Kael Petteesen, Director of the Tromso Arctic Museum, has suggested 

 that the object of polar expeditions could be obtained most easily, surely, and 

 cheaply, by dispatching, instead of single sporadic expeditions, every year, for a 

 period of ten or eleven years, a number of well-equipped steamers from certain 

 suitable points toward the pole. Amid the ever-varying shifting of the polar 

 drifts and currents, some of these vessels might possibly get through. He recom- 

 mends four points of departure for such vessels: one along East Spitzbergen and 

 Franz-Josef Land, and northward; one east of Franz-Josef Land, from the Yeni- 

 sei or Obi ; one by way of Franz-Josef Land, starting from the New Siberian 

 Islands or the Lena ; and one from a suitable spot in Bering Strait. 



