SPECIAL PHYSIOLOGY OF SEX AND REPRODUCTION. 255 



cence is smoothed away. In Solenostoi?ia (allied to pipe-fish) the 

 ventral fins unite with the skin to form a pouch in w^hich the 

 eggs are retained. In other cases, it is the male which incubates 

 or cares for the ova. Not a few form nests, as in the stickle- 

 back, over W'hich they keep a jealous guard. In some species 

 of Arins the eggs are carried about in the pharynx ; while in 

 the sea-horses a pouch is developed on the posterior abdomen. 



Among invertebrates, brood-chambers or cradles for the 

 young are not uncommon. The capsules of hydroids, the 

 tent of spines on a few sea-urchins, the depressions in the skin 

 in one or two sea-cucumbers, the modified tentacles of some 

 marine annelids, the dorsal shell-chamber in water-fleas, the 

 incurved abdomen of higher crustaceans, the gill-cavities of 

 bivalves, the beautiful brood-shell of the argonaut, illustrate a 

 habit even an outline of which is beyond our limits. 



§ 9. Nefuesis of Reproductiofi. — ^Ve have already shown 

 how reproduction in its origin is linked to death. The primitive 

 ruptures by which the protozoon reduces encumbering bulk, 

 saves its own life, and multiplies its kind, are only a step or 

 two from more diffuse dissolution which is death. 



The association of death and reproduction is indeed patent 

 enough, but the connection is in popular language usually 

 misstated. Organisms, one hears, have to die ; they must 

 therefore reproduce, else the species w^ould come to an end. 

 But such emphasis on posterior utilities is almost always only 

 an afterthought of our invention. The true statement, as far 

 as history furnishes an answer, is not that animals reproduce 

 because they have to die, but that they die because they have 

 to reproduce. As Goette says, " it is not death that makes 

 reproduction necessary, but reproduction has death as its 

 inevitable consequence." This of course refers primarily to 

 the incipient forms of both these katabolic processes. 



It is necessary to give a few illustrations. Goette refers to 

 Hgeckel's Magosphcera, a protozoon which just as it had formed 

 for itself a multicellular body broke up into the component units. 

 These lived on, and there was no corpse, but at the same time 

 the multicellular colony was no more. Again he takes the case 

 of the lowly and somewhat enigmatical orthonectids, which 

 Van Beneden has classed as Mesozoa, between the single- 

 celled and the stable many-celled animals. Here the mature 

 female forms numerous germ-cells, and terminates her individual 

 life by bursting. The germs are liberated, the mother animal 



