OBSERVATIONS ON LIVING SPECIMENS. 11 



DEVELOPMENTAL STAGES. 



Too little attention has been paid to the study of the develop- 

 mental stages in the Foraminifera. It has been denied by many 

 authors that such stages as are seen in the tests of many of the 

 multilocular Foraminifera have any significance. If, however, the 

 developmental stages are studied and compared with what is known 

 of the development of the particular group in the fossil series, a 

 close relation will be found. This comparison is somewhat compli- 

 cated by the lack of certain stages in the asexual or megalospheric 

 forms. In the microspheric or sexual form, where the stages are most 

 nearly complete, the comparison leads to a very close relationship 

 between the ontogeny and the phylogenetic history of the group. 

 It seems fair to say that if a careful study is made along these 

 lines, a very complete classification can be developed in many of 

 the families which will rest upon better ground than the present 

 classification. 



The Tortugas collection shows many interesting problems in devel- 

 opmental stages, but they will be considered in this paper only in an 

 incidental way. 



VARIATION. 



Much of the so-called variation in the Foraminifera may be 

 divided into groups. The first of these may be the differences due 

 to the different stages in development and which are no more to be 

 classed as variation than the differences in such molluscan shells as 

 Cyprcea, when the young is a coiled spire and the adult a greatly 

 expanded chamber covering the whole early stages. 



The second of these are the differences due to the two distinct 

 forms, asexual and sexual, or megalospheric and microspheric. These 

 differences should be taken into consideration in eliminating so-called 

 variation. Differences due to these causes should strictly no more 

 be classed as variations than the differences in sexual characters 

 among the higher animals. The third group of characters show 

 true variations. That is, actual size in adults, variations in orna- 

 mentation in adults (not in comparison of young and adult tests), 

 and other like characters. When such characters alone are taken 

 it will, I am very sure, be found that the actual amount of true 

 variation in this group is relatively small. 



An additional cause for much of the so-called variation is probably 

 the failure of many authors to carefully divide species. A study of 

 the Foraminifera from an area such as that of the western Atlantic 

 from Newfoundland to the coast of Brazil shows that many faunas in 

 the region have very definite Hmits, bathymetrically and geo- 

 graphically. Some species are very restricted in their distribution 

 and others more widespread, exactly as in other groups of the animal 



