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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



[VOL. 47 



reproductive cells of only one kind are present, these are found to 

 be ova, though one or two observers have described spermaria only. 

 However when the ova are developed in greatest number they are 

 found to be accompanied by spermaria, so there is good reason to 

 suppose that, as a rule, coral polyps are protogynous. 



Fig. ii. — Three diagrammatic figures illustrating the manner of appearance 

 of the six pairs of mesenteries (a-c) constituting the second cycle. The 

 mesenteries arise in unilateral pairs within corresponding exocoelic chambers on 

 each side of the polyp. At first (a) a pair appears within the dorso-lateral 

 exocoele on each side; shortly after (b) a similar pair arises within each 

 middle exocoele ; then (c) a pair within each ventro-lateral exocoele. For a 

 long time the pairs retain a difference in size, corresponding with their order 

 of appearance. The sequence is that followed in the development of larval 

 polyps of Siderastrea radians. 



In some few cases the extrusion of free ova and spermaria has 

 been observed, but it may be questioned whether such instances are 



