xxii INTRODUCTION. 



separate, and inclose the reproductive organ (/), uniting 

 again beyond it into a second mesentery (g), which is 

 bounded by the craspedum (h) presently to be described. 

 Both mesenteries are full and plaited, especially the eras- 

 pedal one. 



The spermatic fluid is discharged in a turbid cloud 

 through the mouth, and is diffused through the surrounding- 

 water (pp. 99, 100). The ova are also discharged through 

 the mouth, or through the gonidial grooves (pp. 97, 98, 99). 

 The development of the egg is into an infusorium-like 

 germ, differing in shape in different species, but always 

 covered with vibratile cilia, and freely locomotive. Exam- 

 ples of the occurrence of these will be found infra {passim), 

 and many highly interesting details have been recorded in 

 the magnificent works of Sir J. G. Dalyell. The manner 

 in which the development of the Anemone proceeds has 

 been illustrated by Dr. Cobbold;* a depression in the 

 surface of the globose embryo becomes the general cavity ; 

 the edges then become incurved and descend into the cavity, 

 forming the stomach ; septa spring from the inner wall, 

 beginning from the summit and extending downwards, and 

 tentacles bud from around the mouth. Eggs, germs, or 

 fully formed young, are discharged indifferently through 

 the mouth : in the latter two cases the embryos have passed 

 their earlier developments within the general cavity. 



7. Teliferous System. In common with some nearly 

 allied forms the ACTINARIA are furnished with a system of 

 armature of most extraordinary character. It is compara- 

 tively a recent discovery that their tissues contain exces- 

 sively minute bodies, in the form of oblong or oval transpa- 

 rent vesicles, which have the power of shooting out a long 

 thread of extensive tenuity. Wagner first drew the atten- 

 tion of physiologists to these organs, though he mistook 

 their functions for that of spermatozoa ; an error which was 

 participated by Dr. Wyman, in his observations recorded in 

 Dana's magnificent work on Zoophytes. Their true cha- 

 racter has, however, been sufficiently established by many 

 observers, including Wagner, Erdl, Quatrefages, Kolliker, 

 Agassiz, and myself. These bodies I have called cnidai, 

 or thread-cells. 



The cnidce, in the Actinoid Zoophytes, are not confined 

 to one organ or set of organs. They are found in various 

 * Annals Nat. Hist, for Feb. 1853. 



