HYDRO IDS AND JELLY-FISHES. 



39 



No. 28. 



No. 29. 



There is one of these Hydroids living as a single 

 animal, not in a community or cluster like the one I 

 have described, which is excessively small, 

 perhaps half an inch high, and yet produces 

 some of the largest Jelly- Fishes. It does not 

 bear them by buds or eggs, as I shall show 

 you, but by dividing itself into a succession 

 of animals, each one of which is a Jelly- Fish. 

 Here is a picture of this Hydroid somewhat magnified, 

 and before this process begins (No. 28) ; and here is 

 another picture of the same after it 

 has begun to divide, and very much 

 enlarged, in order to show you how 

 this change takes place (No. 29). 

 After the little Hydroid has lived 

 for a time as you see him in the first 

 picture, that is, as a single animal attached to the rocks 

 or sea-weed, the upper part be- 

 gins to contract, then another con- 

 traction takes place a little lower 

 down, and so on till the whole 

 animal is divided by contractions 

 through, all its length, and it looks 

 something like a pile of saucers 

 (No. 30).* Then each one of 

 these contractions deepens more 

 and more, till each part that has 

 been so marked off separates from 

 the rest, and swims away a free ani- 

 mal, shaped like the picture on the next page (No. 3i).1 



* No. 30 : Strobila. 



t No. 31. This jelly-fish has been described as Ephyra. 



No. 30 



