^'o. 2308. LIVING SPECIMENS OF IRIDIA DIAPHANA—CUSHMAN. 157 



With each increase in the size of the test the inclosing wall of the preceding stage 

 is absorl)ed so as to leave an undi\ided ca\dty, the shape of which varies according 

 to the direction and manner in which additions to the original chamber have been 

 made. 



In the case of the Tortugas specimens attached to the leaves of 

 Posidonia several inches above the bottom it is difficult to see 

 ^Yhere new material for growth is acquired. The habit which has 

 already been noted, of leaving the test and moving about as a nalved 

 mass of protoplasm, may easily account for this change in material. 

 While in this free state new material from the bottom may easily 

 be ingested and carried about until a new attachment is made. 

 Such specimens were placed in a mass of debris composed of fine 

 sand and fine fragments of glass wool, but although some of this 

 material was taken into the body, no new test vv^as formed in any 

 of the specimens kept in confinement. 



Some specimens were killed and stained, but only one of these 

 seemed to show a definite nucleus that is shovm here (pi. 19, fig. 1). 

 It has a very large nuclear mass with a definite nuclear membrane 

 surrounded by a large mass of ectoplasm, in which are numerous 

 food particles. 



The most interesting observations are the rapid motion, the 

 individual character of specimens when in contact, and the power 

 of leaving the test at will. 



EXPLANATION OF PLATES. 

 Plate 19. 



Fig. 1. Animal of Iridia diaphana, test dissolved away, leaving the protoplasmic 

 mass with a single large nucleus, nuclear wall, an irregular mass of ecto- 

 plasm containing a few symbiotic algae, and food particles, X 100. Speci- 

 men killed and fixed in corrosive sublimate and glacial acetic acid, stained 

 in haematoxylin. 



2. Portion of test at periphery from below, X 50. Central mass of protoplasm 



with very few algae, most of them being near the peripheral portion and in 

 the radial canals leading from the central mass to the periphery of the 

 test. This specimen was quiescent and showed no pseudopodia at the 

 time it was drawn. 



3. A branching mass of pseudopodia irregularly bifurcating, mainly composed 



of clear protoplasm, but with numerous more concentrated masses and a 

 few of the unicellular algae. 



Plate 20. 



Fig. 1. Elongate flattened mass udth numerous pseudpodia traveling toward the 

 direction of the larger end, X 50. 

 2-6. Various stages in the progress of the same indi\'idual in a thicker, more nearly 

 rounded form. 



