156 University of California Publications in Zoology. [Vol. 6 



as will be noted later. Before the vascular canal disappears, the 

 nourishment reaches the zooids by way of the blood tubes. 



The disappearance of the blood tubes begins at the distal end 

 of the block. If zooids are removed from different portions of a 

 large block the canal opening (fig. 3, v) will be seen to be much 

 smaller at the distal end of the block than at the proximal end. 

 If this gradual disappearance is brought about in such a way 

 as to still allow a continuous circuit through the portion of the 

 canal that remains at any given time the younger, proximal 

 zooids will receive nourishment from the parent for a longer 

 period than the more distal ones. 



The possibility still remains that there may be a transfusion 

 of nourishment between the zooids by way of the papillae or by 

 protoplasmic connection at this point, but there is no sure 

 evidence to this effect. 



4. QUANTITATIVE OBSERVATIONS AND DATA. 



In choosing the zooids for measurement, the terminal block 

 only was taken from any chain, as the vascular connection in the 

 younger blocks is too intimate to allow the zooids to be separated 

 without mutilation. In the case of the first five blocks measured, 

 only one measurement was taken of each dimension. The zooids 

 were removed one at a time, first from one row and then from 

 the other. These first zooids were not kept after being measured. 

 The measurements were made with the ocular micrometer in the 

 Zeiss binocular microscope (ocular 2, low power objective). A 

 unit in the table is equal to 0.1 mm. and the scale could be read 

 to 0.5 of a unit or 0.05 mm. In entering the results in the tables, 

 each row of zooids in the block was treated as a separate series, 

 so that from the five blocks first measured I have ten series of 

 measurements. (Table 1.) 



In obtaining the data for the three later blocks (table 2). a 

 greater effort was made to avoid errors. In the first place, 

 it seemed desirable to complete the measurement of a series 

 all at one time to avoid changing conditions of light, etc., as far 

 as possible. As it takes considerably more than four hours to 

 separate the zooids of a block and measure them, they were first 

 separated and each put into a bottle containing the number of 



