8 BULLETIN 71, UNITED STATES NATIONAL MUSEUM. 



has not definitely been observed in this group. The empty tests left 

 behind must form a large proportion of the dredged Foraminifera. 

 The two forms may be distinguished by the size of the proloculum and, 

 when sufficiently known, by other characters as well. 



The microspheric form is thus the result of a conjugation or a sexual 

 process, while the megalospheric form is the result of simple division 

 or an asexual process. As a rule the megalospheric form is by far the 

 more common, and in many species the microspheric form is very 

 rare, or even as yet unknown. The microspheric form, while it starts 

 as a smaller individual, in most cases attains a much larger size than 

 the megalospheric, as might be suspected from the nature of the re- 

 productive processes by which it is formed. In species where there 

 are definite stages in development it is usually the microspheric form 

 which repeats these most fully, these stages being reduced or entirely 

 skipped in the megalospheric form of the species. 



In some cases the megalospheric form may give rise to a group of 

 megalospheric young instead of to zoospores. On the whole, the life 

 cycle agrees well with the alternation of generations as seen in certain 

 other groups of animals. 



. PELAGIC FORAMINIFERA. 



All of the Foraminifera may be divided into two classes, those 

 which are known to live at the surface, relatively a small number, 

 and those which have been found only on the bottom, which form 

 the great majority. 



The pelagic species number but little more than twenty, and of 

 these few ace really common at the surface. The two genera which 

 have more than a single species are Globigerina and Pulvinulina. The 

 following species have been taken at the surface: Globigerina sequi- 

 lateralis, G. bulloides, G. conglobata, G. digitata, G. dubia, G. iiiflata, 

 G. marginata, G. sacculifera; Pulvinulina canariensis, P. crassa, P. 

 menardii, P. patagonica, P. truncatulinoides , P. tumida; Hastigerina 

 pelagica; Orbulina universa; Candeina nitida; Pullenia obliquelocu- 

 lata; Sphseroidina dehiscens; Cymbalopora bulloides; and Chilostomella 

 ovoidea. 



Of these species a few have been observed but once as single 

 specimens, and at best are but doubtful members of this group. 

 Others are almost never found on the bottom, and may be considered 

 as truly pelagic species. 



As a group the pelagic species are characterized by peculiar struc- 

 tures. In Hastigerina pelagica, for example, there has been noted a 

 peculiar vacuoled condition of the protoplasm, in which it extends out 

 from the body to several times the diameter of the test and is filled 

 with large vacuoles. Many of the species have large apertures, and 

 in some cases a number of secondary ones are present, especially in 



