1902.] NATURAL SCIENCES OF PHILADELPHIA. 789 



his orders " TrachomedusjB " and " Leptomedusse " are not justi- 

 fied. 



2. Dehiscence occurs in Gonionema with precise periodicity, and 

 is definitely affected by changes in light. 



3. Segmentation is total and equal ; endoderm is formed by 

 delamination of the blastomeres; a solid morula results. 



4. A planula stage occurs, and later a hydra stage, in which the 

 polyp develops first two tentacles, later a second pair. 



5. Youngest medusse and oldest polyps show marked homologies ; 

 direct metamorphosis is suggested. 



6. Peculiar ])athological phenomena occur, the larva living for 

 weeks in the form of a plasmodium, with amoebiform activities. 



7. Alternation of generations occurs. A non-sexual form of 

 multiplication appears, during larval life ; buds are produced which 

 are detached as planulse and go through the same changes as the 

 parent. 



8. The order and arrangement of tentacles in the gonosome 

 follows a definite plan of cyclic sequence, producing a figure which 

 is cyclically, not bilaterally, symmetrical. Tentacles and sense- 

 organs appear at determinate points on the bell margin. 



9. Histogenesis of tentacles and sense-organs shows their 

 homology 



10. The origin of nematocysts from the ectodermal pad at the 

 base of the tentacle is described. 



11. Gonads arise as enlargements by proliferation of the ecto- 

 dermal subumbral epithelium of the radial canal. 



DESCRIPTION OF PLATES XXXI-XXXIV. 



T7ie figures, except tJiose otherwise noted, have bee/i drawn by the author. 



Plate XXXI, Fig. 1. — Adult Oonionema in resting attitude ; floating 

 after a period of active swimming. 2/1. 



Fig. 2. — Medusa m act of swimming ; bell contracted, tentacles 

 drawn up at the end of a forward impulse. Photographed 

 from life. 1/1. 



Fig. 3. — Photograph of medusa inverted and clinging to the 

 bottom. 



Fig. 4. — One radial canal from ripe male, showing gonad, c, cir- 

 cular canal ; r, radial canal. 8/1. 



Fig. 5. — Gonad of female, during dehiscence. 20/1. 



Fig. 6. — tCgg during first segmentation ; cleavage furrow half 

 completed. 570/1. 



Fig. 7. — Egg during second segmentation, left hemisphere com- 

 pletely divided, right hemisphere in process of dividing. 



