FORAMINIFERA OF NOLiH PACIFIC OCEAN. 7 



often of a much lighter color than the rest of the test; on the other 

 hand, in other forms, as in Hormosina ovicula, the tips of the chambers 

 are often much darker than the rest. In the chitinous tests the usual 

 yellowish-brown color of chitinous structures is present, and is some- 

 what variable in its tone. 



In the secreted calcareous tests the usual color is white when empty. 

 There are various exceptions, a reddish or pinkish color being most 

 common, such as appears in Globigerina rubra and Truncatulina rosea, 

 or perhaps more pronounced in Polytrema minaceum. In other cal- 

 careous species, as in various species of Discorbina, there is a brown 

 color rather prominently developed. This is often confined to the 

 earliest chambers, and the later ones may be white. In many species 

 when alive there is probably more or less color which disappears when 

 the test is empty. 



LIFE HISTORY. 



For many of the Foraminifera two distinct phases have been dis- 

 covered. One of these — the microspheric form — has a proloculum or 

 first chamber of much smaller size than the other — the megalospheric 

 form. These two forms are to be looked for in all species. 



The microspheric form has a number of nuclei, often a larger number 

 than there are chambers, scattered irregularly through the protoplasm 

 of the bod} T . There seems to be a rather definite relation between the 

 size of the nuclei and the size of the chamber in which they occur, the 

 larger nuclei being in the larger chambers and the reverse. Appar- 

 ently these nuclei simply divide in their reproduction during the 

 growth of the test. 



When the animal attains its adult stage there is a great increase 

 in the number of pseudopodia, and the entire protoplasm either leaves 

 the test and accumulates about the exterior or is drawn into the 

 outer chambers. Finally, each nucleus gathers a mass of protoplasm 

 about itself and secretes the proloculum of a new test. This newly 

 formed proloculum is of the larger type and is the first chamber of the 

 megalospheric form, instead of being of the same size as that of the 

 microspheric parent from which it was derived. The megalospheric 

 form differs from the microspheric form in having a single nucleus. 

 This does not divide, but moves along as new chambers are added, 

 keeping in about the middle chamber numerically. Nucleoli appear 

 in increasing numbers as the growth continues, and finally the whole 

 nucleus breaks down and a great number of minute nuclei appear. 

 These draw about themselves portions of the protoplasmic mass and 

 then divide by mitotic division. Finally, the mass leaves the test in 

 the form of zoospores. These are then supposed to conjugate and 

 to give rise to the small proloculum of the microspheric form, thus 

 completing the life cycle, although the actual process of conjugation 



