l8 MARINE BIOLOGICAL LABORATORY. 



cells, etc., are replaced by deeper and younger cells, 

 called ''intermedial." The reproductive cells have the 

 same origin. 



The work of reproduction then is not confined to any 

 one or two classes of cells ; it is divided and sub- 

 divided in endless detail, carried all through the organ- 

 ism, and distributed independently of most other labors. 

 Its elaboration in this or that direction may be cor- 

 related with a system of morphological differentiations, 

 so extensive and involved that a whole course of lectures 

 would be required to elucidate the subject. Take the 

 genital system of the vertebrates, or that of forms no 

 higher than the annelids, and you will find no end of 

 problems yet to be settled. What complicated cycles 

 of generation have been followed by many parasitic 

 forms, especially among the worms, and what wholesale 

 modifications of structure in answer thereto. How 

 devious have been the paths of generation in insects, 

 and how wonderful the metamorphoses attending them. 

 How diverse the ways of multiplication among the 

 Tunicates and Coelenterates, and what puzzling suc- 

 cessions and combinations of forms have here tried the 

 sagacity of naturalists. 



What peculiar corporation aggregates are represented 

 in Siphonophore colonies, of which we have a most 

 beautiful example in the Portuguese-man-of-war. How 

 long it has taken to decide between the ''poly-organ 

 theory" of Eschscholtz, Huxley, M tiller, and Met- 

 schnikoff, and the "poly-person theory" of Vogt, 

 Leuckart, Kolliker, Gegenbaur, and Haeckel. The 

 complex of reproductive processes in one such colony 

 would still bear a life-time of research, and not be 



