THE LOWER FORMS OF LIFE. 101 



from this that they have no "thread cells," as they would in such 

 minute creatures evidently be too small and delicate to pierce the 

 thick human skin. It is certain, however, that the genera Turris, 

 Oceana, Dianea, and Thaumantias are all phosphorescent. This 

 phosphorescence must not be confounded with that produced by 

 terrestrial animals like the glowworm and lantern fly, in whom a 

 special apparatus exists, and which is evidently designed, in the 

 one case at least, to guide the male to its mate. The same result 

 may be produced by very different means, and we often see this 

 in our study of Nature and her laws. All analogy points to the 

 probable inference that the power of emitting light is given to the 

 lowly and graceful Medusa as a means of protection from danger. 

 The subject is one of interest and importance, and I commend it to 

 the study of those who have the time and opportunity for such 

 investigation. 



THE EEPRODUCTION AND DEVELOPMENT OF THE HYDROZOA next 

 claim our notice, and the facts to which I beg the particular attention 

 of those who study natural science are very curious and interesting. 

 I have before detailed one of the modes by which the common fresh- 

 water Hydra is reproduced viz., from buds like a plant. But the 

 creature which thus increases itself by buds was itself the product 

 of an egg ! Such at least, I ought to have said, might have been 

 its origin, for the Hydrse multiply by eggs as well as buds. Yet a 

 third way remains to be mentioned by which these singular creatures 

 can be reproduced. They can divide themselves into one or more 

 parts by what is termed fissiperation. "We are told by a German 

 writer, Jager, that he has observed specimens which he had kept 

 warm divide themselves into different portions, each of which 

 became encysted like Vorticella (ante, p. 33). Jager suggests that 

 these encysted portions of Hydrse would hybernate in this con- 

 dition, and in the spring each would come out a veritable fully- 

 formed Hydra. Although Jager has not, I believe, substantiated 

 the truth of this suggestion, all analogy gives it a higher degree of 

 probability. A great deal of the surprise which these statements 

 create is removed when it is considered, first, that all eggs or ova are 

 more or less of the nature of buds themselves ; and, secondly, that 

 even as high in the scale as insects, the development of young may 

 take place by internal budding without the direct intercourse of the 

 sexes.* Every practical entomologist knows this. Bearing these 

 facts in mind, let us look at the details in the life history of the 



* This fact, as far as the aphides are concerned, has been lately rendered 

 doubtful by the experiments of the physiologist Balbiani, who considers all tho 

 apterous aphides as true hermaphrodites. 



