450 BIOLOGY OF THE PROTOZOA 



red sporangia are known. In most cases the "spores" are uninu- 

 cleate, but forms with two and with four nuclei are known. 



In some cases the simultaneously formed sporangia unite to form 

 a common fruiting body in which the individual sporangia may still 

 be distinguished in some types. In other types, however, this inde- 

 pendence is lost and one common fruiting body results, with one 

 continuous capillitium. Such fruiting bodies are called aethalia. 

 (See Key for further classification.) 



Sub-class III. FORAMINIFERA d'Orbigny. 



(Reticulosa, Thalamophora.) 



This group of the rhizopods includes a large number of bottom- 

 dwelling and marine Sarcodina with anastomosing pseudopodia 

 (myxopodia). A few forms live in fresh water (Allogromia species), 

 and some forms are pelagic in the sea (Globigerina, etc.). The great 

 majority are provided with tests composed for the most part of 

 calcium carbonate. In some, however, the test is purely organic, 

 consisting of substance of gelatinous or pseudochitinous character 

 (Allogromia); or foreign particles of sand, diatom shells and detri- 

 tus of one kind or another, may be cemented to the pseudochitinous 

 test by gelatinous or chitinous cement. Such tests are usually 

 described as arenaceous, in contrast with the clear lime shells or 

 porcellaneous types. The walls of the shells are either thick and 

 homogeneous or are perforated by minute pores (foramina) through 

 which single pseudopodia are protruded. The cavity of the shells 

 may be a single chamber, septa if present being incomplete (Mono- 

 thalamous). Or a multitude of chambers may be present, separated 

 by partitions or septa (polythalamous). The latter may be compli- 

 cated by secondary deposits of lime through which labyrinthine 

 canals and passages give occasion for intricate designs (Fig. 74, 

 p. 1-38). The surfaces of the shells are usually smooth but in some 

 forms, particularly the floating types of Globigerina, spines, ridges, 

 rays, etc., probably assist in floating. 



The living substance is usually so fluid that it is rarely quiet and 

 protoplasmic streaming is so characteristic that the Foraminifera 

 have been favorite materials for the study of protoplasm. It is not 

 divided into zones, and the marine forms have no vacuoles. There 

 are numerous foreign bodies as a rule and aggregates of the residue 

 associated with food substances, form masses of fecal material 

 termed "stercome." In many forms living commensals are also 

 present in the form of small yellowish Cryptomonas-like forms 

 (Chrysidella) which are liberated with sporulation of the host 

 organism. 



The living protoplasm fills more or less completely all chambers 

 of the organism. In polythalamous forms protoplasmic strands 



