NO. 9 RESEARCHES OF JOSEPH JACKSON LISTER HERON-ALLEN 5 



bottom and may be clearly seen when in bright light, with a black 

 background. Usually one or two of the terminal chambers contain 

 little protoplasm and appear empty. In the ordinary condition their 

 pseudopodia are inconspicuous, but they may generally be detected 

 with a pocket lens, extending in sheaves from the shell,^ and with 

 a microscope they have the usual appearance of delicate straight threads 

 with granules. 



In some 50 cases I have seen examples in the I'c productive phase. 

 The first sign of this phase is seen in the character of the pseudopodia.' 

 Instead of being disposed as above described, the pseudopodia are 

 limited to a circular or oval area immediately about the shell, the 

 center of the area being the mouth of the shell, which is nearly always 

 flat against the glass. This area is covered completely by a close web 

 of radiating and interlacing pseudopodia, and its limits are fairly 

 sharply defined. The pseudopodia are so thick as to intercept the 

 light, giving rise to the appearance of a semi-transparent milky 

 halo about the shell. This may be called the " premonitory halo." It 

 is readily seen by the naked eye. 



The animals are generally found in this condition in the early 

 morning. 



In nearly all the cases that I have observed the halo has been 

 established by 6 : 30 a. m." 



After the animal has remained in this condition for some hours, 

 the protoplasm begins to leave the shell, the strands of the pseudopodia, 

 especially the radiating ones, become thicker, and the protoplasm 

 withdraws itself, first from the peripheral ends of the outer whorl of 

 chambers, being massed in the terminal chambers. Gradually the pro- 

 toplasm leaves the shell, passing through the direct communications 

 between the chaml^ers. and also, as is seen in specimens preserved at 

 this stage, through the canals which exist in the walls separating the 

 chambers from one another. The protoplasm is generally brown, owing 

 to the presence of brown granules.* As the protoplasm emerges into 

 the area of the halo, this becomes streaked with brown, at first in 



' When they are observed immediateh' after the jet of water has been playing 

 into the jar, a long sheaf of the pseudopodia is seen pointing towards the current 

 set up in the water. After the water has become still, they are shorter and point 

 in various directions. J. J. L. 



'This was first observed on June 21, 10: 30 a. m. 



' While these observations were in progress, Lister frequently remained all 

 night in the Laboratory of the Marine Biological Association. 



* I : 30 p. m. 



