238 Tlie Unit I) of the Organism 



reproduced in many of the larger textbooks and handbooks, 

 Biitschli in j^a-rticular giving specially good figures. The 

 remarkable resemblance of the shell of this and of allied 

 genera to the shell of the chambered nautilus has long been 

 a common subject of remark. According to the prevalent 

 view, althougli the variety and complexity of the shells of 

 great numbers of foraminiferae are universally recognized, 

 they do not militate against the conception of the animals 

 as "simple," because they are only secretory structures, or 

 in many groups only structures built up from foreign sub- 

 stances. But what right have we, I ask, to assume but slight 

 protoplasmic differentiation in a creature that can produce 

 in an}' way whatever such a system of chambers and septa 

 and canals and pores, as is presented by the shell of Oper- 

 cidina? This query becomes particularly searching when 

 one considers that each of the various genera and species 

 has its own type of shell. 



In his Monograph of the Forammifera of the North Paci- 

 fic Ocean Dr. J. A. Cushman remarks that being single- 

 celled animals, the structures of the Foraminifera "do not 

 need explanation on the basis of organs and tissues." ^ This 

 naive manner of dodging difficulties is characteristic of clc- 

 mentalist notions about explanation — the method of making 

 an implied theoretical definition take the place of searching 

 examination. The particular difficulty evaded by definition 

 in this case pertains to the nature of the outer portion of 

 the protoplasm or sarcode, which constitutes so large a 

 fraction of the living body of both the Foraminifera and the 

 Rhizopoda. As is well known, the sarcode produces the 

 shell either by secretion or by the selection and placement 

 of foreign particles. In many Foraminifera, as OpercuUna, 

 the sarcode extends over the whole exterior of the shell, 

 thus making the shell an internal structure. The highly 

 elaborate canal and pore systems above referred to are 

 passage-ways for the semi-fluid sarcode. 



