THE MICBOSCOPIST IN BERMUDA. 129 



It is not however the case that all the Hydrozoa produce free- 

 swi mining medusae ; for instance this Sertularia, which I will show 

 you later under the microscope with its beautiful white-beaded 

 reproductive capsules, retains the generative medusoid forms 

 within these capsules, and emits only the ciliated gem mules which 

 are produced from them. On the other hand some of the 

 medusae do not generate the branching Hydrozoa. There seem 

 to be all gradations in the relations between these two kinds of 

 beings. And it is a matter of surprise, seeing that the connec- 

 tion is not necessary either to one or the other, that natural 

 selection, if it operated at all between them, has not long ago 

 dissolved all connection whatever. 



But I have not time to describe more of the marvels of the 

 marine invertebrate kingdom. To me it is by far the most in- 

 teresting province of natural history. The world had passed 

 more than half of its living age before animals began to have a 

 bony skeleton. The fishes of the Devonian strata, which is the 

 formation next below the coal measures, were the first creatures 

 that possessed anything like a bony structure. All the animals 

 before these were invertebrates ; and they abounded and held 

 sway while the sea was depositing in places ten miles of the 

 thickness of the earth's crust. All the rocks that are below us 

 where we are to night, were formed before ever there was a ver- 

 tebrated animal in existence. The invertebrates belong then to 

 the most ancient families of the world. They are the last sur- 

 viving representatives of the oldest inhabitants. While all the 

 higher races have been progressing from grade to grade, these 

 have always remained the same, except in a few changes of dress 

 and externals. 



They tell us of the prevailing conditions of life in the earliest 

 geological ages ; for the spheres they filled and were adapted to 

 then, are the restricted spheres they fill and are best adapted to 

 now. The same environments have followed them down in their 

 gradually diminishing numbers from the Silurian age to the 

 present time. They tell us of the earliest fashions of growth 

 and of reproduction ; when animals budded and sprouted like 

 plants ; when instead of pairs, it took triplets to carry out the 

 great behest " to go forth and replenish the earth." 



