THE FORAMINIFERA 77 



sphaerium, the meeting and conjugation of zoospores from different 

 parents is necessary for the production of a microsphere. 



It is very desirable that the conclusion should be confirmed 

 by direct observation, but, meanwhile, it seems not premature to 

 admit that it is probable that the microsphere arises from the 

 conjugation of zoospores. 



We may conclude, then, that the microspheric aad megalo- 

 spheric forms of the Foraminifera represent alternating or re- 

 curring generations in a life -cycle. While the megalospheric 

 generation arises asexually, either from a microspheric or a megalo- 

 spheric parent, it is probable that the microspheric generation 

 arises sexually i.e. by the conjugation of two similar zoospores. 



Representatives of the two generations have been recognised 

 in species belonging to the following genera of Foraminifera : 



ORDER l. Gromiidea (7). 1 



( 2. Astrorhizidea. 2 ) 



( 3. Lituolidea.) 



4. Miliolidea. 



Family MILIOLINIDAE. Cornuspira (24, 1898, p. 612); Spiro- 

 loculina (57, p. 201); Biloculina (27, p. 863); Sigmoilina (Planispirina, 

 pars), Schl. (53, p. 106) ; Triloculina and Quinqueloculina (27, pp. 863 

 and 1598); Massilina (57, p. 218); Adelosina (52, p. 91); Idalina 

 and Periloculina (28) ; Lacazina (27). 



Family HAUERINIDAE. Planispirina, Seg. (56, p. 194). 



Family PENEROPLIDIDAE. Peneroplis and Orbiculina (this article), 

 Orbitolites (4, p. 693, and this article) ; Meandropsina (59). 



Family ALVEOLINIDAE. Alveolina (51, p. 526). 



ORDER 5. Textularidea. 

 Family TEXTULARINAE. Textularia and Spiroplecta (this article). 



(ORDER 6. Chilostomellidea.) 

 7. Lagenidae. 



Family NODOSARIIDAE. Nodosaria and Dentalina (51, p. 626); 

 Frondicularia (15, p. 480) ; Cristellaria (?) (5, p. 45). 



Family POLTMORPHINIDAE. Siphogenerina (Sagrina) (50, p. 21). 



(ORDER 8. Globigerinidea.) 

 9. Rotalidea. 



Family ROTALIDAE. Rotalia (51, p. 526, and 20, p. 436); 

 Truncatulina and Calcarina (20, pp. 436 and 437). 

 Family TINOPORIDAE. Polytrema (23). 



1 The cases of Hyalopus and Mikrogromia are considered below. . 

 3 In the orders included in brackets I have not succeeded in finding a record of 

 the existence of dimorphism. 



