118 J. J. LISTER. 



" endogenous gemmation," and the microspheric young of "ecto- 

 genous fission." Both processes it is conceived might be going 

 on simultaneously in one individual. The author has unfor- 

 tunately revived, in support of his hypothesis, the old idea of 

 the individual distinctness of the contents of the different 

 chambers of the foraminiferan shell. Apart from this, however, 

 the view as to the mode of origin of the two forms of young 

 cannot be accepted as correct. For, as will be shown below, in 

 the cases in which the origin of the megalospheric young has 

 been traced (Polystomella, Rotalia), they have arisen by the 

 multiple fission of the whole of the protoplasm of the parent. 

 The exact origin of the microspheric form is still unknown, but 

 the zoospores from which it is probably in some way derived, 

 are also produced (in Polystomella) by the multiple fission of 

 the parent protoplasm. 



(6.) The Relation of Orbulina and Glohigerina. 



The featui-es presented by Orbulina have been much dis- 

 cussed (c/. BitTSCHLl (6), pp. 68-70), and as they have been 

 supposed to exemplify the phenomenon of dimorphism, the 

 subject claims our notice here. 



PouRTALES (28) first drew attention, in 1858, to the fact 

 that a spirally arranged group of chambers, resembling the 

 complete shell of a Glohigerina, is often found within the 

 spherical shell of Orbulina {cf. wood-cut, p. 119). This he 

 considered to be the young of Orbulina, and he suggested that 

 Globigerina and Orbulina might be alternate generations in the 

 life-history of one species. 



In 1868, Major OwEN (27) stated his opinion that the 

 Orbulina shell " may be regarded as a wild-growing closing-in 

 chamber " of the Globigerina. 



In 1883, ScHACKO (29) described specimens of Orbulina, 

 both recent and fossil. He showed that the Orbulina shell is 

 sometimes double ; that the contained Globigerina shell is most 

 fully developed when the Orbulina shell is small, and that in 

 large (dry) specimens a heap of thin-walled fragments is often 



