ON THE LIFE- HISTORY OF THE FORAMINIFERA. 115 



While agreeing that the two forms constituting a "pair" 

 resemble one another in the external sculpturing, he points out 

 that examples intermediate in size between them do occur, and 

 also small examples with a small central chamber. It is also 

 shown that the two forms differ in the characters of the 

 chambers which make up the inner whorls as well as in the size 

 of the central chambers. "While the view that one form results 

 from the modification of the other is thus shown to be unten- 

 able, it is suggested that they might with more reason be 

 regarded as representing two sexes of a species. The authors, 

 however, do not definitely abandon the old idea of the specific 

 distinctness of the two forms. 



In 1883, Munier-Chalmas and Schlumberger (25) com- 

 municated to the Academic des Sciences the fact that the 

 phenomenon of dimorphism occurs also in several species of the 

 Miliolidse. Thus, in Biloculina depressa, d'Orb., there are two 

 forms (see wood-cut, p. 114): A, with a large central chamber 

 200-400/* in diameter, and with an outside diameter of the 

 shell of 2' 10 millim.; and B, with a small central chamber 20 /^ 

 in diameter, and an outside diameter varying from 1"5 millim. 

 to 2'64 millim. The interesting fact was also brought forward, 

 that in this group there is a very marked difference in the 

 mode of growth of the two forms. While in the form A, the 

 arrangement of the chambers following the central one is 

 biloculine from the first, in the form B the chambers following 

 the minute central chamber are arranged at first on the 

 quinqueloculine plan, the biloculine arrangement not being 

 attained, in B. depressa, until the eleventh chamber is formed. 



A similar dimorphism is stated to exist in the genera 

 Dillina, Lacazina, Fabularia, Triloculina, Trillina, Quinquelo- 

 cidina, Pentellina, Eeterillina, and Alveolina among the Imper- 

 forata, and among the Perforata in the genera Nodosaria, 

 Dentalina, Siphogenerina, Rotalina, and Amphistegina. 



In the same year ScHACKO (29) described a dry specimen of 

 Peneroplis protms, d'Orb., many of whose chambers contained 

 numbers of young shells. These consisted of an oval central 

 chamber measuring some 35 fi in long diameter, and a canal- 



