ACTINOZOA. 169 



9. ]fepro«1uetive Organs. — The reproduc- 

 tive organs, in most Alcyonaria and Zoantharia^ 

 agree, both as to position and striictiire, with the 

 same parts in Actinia; each spermarium or ova- 

 rium consisting of a prolongation of the peritoneal 

 membrane which clothes the sides of the mesen- 

 teries, and forms along their free edges a double 

 band, within which true generative elements are 

 produced {Ji<j. 26, c). Each band usually con- 

 tains only ova or spermatozoa, but ovaria and 

 spermaria may occur either in the same or in 

 different pol3T)es. Cerkinthus and some other 

 forms are monoecious, but more frequently, as in 

 the majority of Sea-anemones, the sexes appear 

 to be distinct. Not so, however, the Ctenophora, 

 in which group bisexuality may certainly be said 

 to prevail. An ovarium and spermarium occur as 

 thickened folds along the opposite sides of each 

 ctenophoral canal, beneath its endodermal lining. 

 But the same mesentery gives rise on both of its 

 free sides to only one kind of generative element. 

 Here, as in other Actinozoa, the male and female 

 organs differ in their contents alone. 



The ova of the Actinozoa are, in general, of a 

 rounded form, smooth or dilated, and often bril- 

 liantly coloured. Their structure is typical, pre- 

 senting the parts common to ova in general. The 

 spermatozoa are caudate, with a broadly conical 

 or even heart-shaped body, to the apex of which 

 the tail is usually attached. 



Eeproduction does not, as in so many Hydrozoa, 

 devolve upon specially ^modified zooids. Some 

 Actinozoa have been known to become everted 

 and die shortly after the maturation of their genital 

 products. But in others, no such exhaustion 



