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PACIFIC SCIENCE, Vol. XX, April 1966 
and tentacular (type B) stages are accounted 
for. Although this strengthens his one species 
concept, its proof rests in: (1) the ability to 
demonstrate conclusively that frustules (Fig. 13 
A-B) or frustule fragments (C) of a tentacu- 
lar hydranths can metamorphose into tentacular 
hydranths (Fig. 1 4A), and (2) that tentacular 
hydranths (Fig. 14 B) can metamorphose into 
atentacular hydranths (Fig. 13D). If this cannot 
be demonstrated, then two similar but different 
species must exist. 
To prove or disprove this, a more detailed 
and accurate study of frustules was needed. Pre- 
viously, these had been collected from mixed 
cultures; now they must be obtained from cul- 
tures rigorously isolated. Therefore, careful pre- 
cautions were taken against contamination. 
II. THE RELATIONSHIP BETWEEN CERTAIN 
ATENTACULAR AND TENTACULAR STAGES 
A complete set of equipment was placed in 
each of separate but adjoining rooms in the 
laboratory. This consisted of Petri dishes, pip- 
ettes, dissecting needles, thermometers, etc. Each 
set remained in its respective room and was 
checked before each day’s work. Each room had 
its own Aeolosoma hemprichi cultured on rice- 
agar plates following the method of Brandwein 
(1937), and its own supply of aged tap water 
and pond water filtered through millipore filters 
of 0.45 jui pore size. 
Although they were not absolute safeguards 
against contamination of one culture with an- 
other, results proved these precautions adequate. 
Frustules were collected and cultured from 
previously isolated cultures. The number of 
atentacular and tentacular cultures was restricted 
to 20 each, from which the following informa- 
tion was obtained: (1) type of culture; (2) 
length, width at thicker end, width at thinner 
end; (3) change in shape; (4) size of frustule 
divisions; (5) change in position (he., hori- 
zontal to vertical); (6) change in location (i.e., 
locomotion; and (7) date of capitulum or ten- 
tacle formation. 
Previously, measurements in microns of the 
first frustule observed in each of 20 mixed cul- 
tures showed these variations: lengths 575-75, 
mean 375; widths, thicker end 125-37, mean 
87; widths, thinner end 75-37, mean 54. 
Figure QA shows this frustule drawn to the 
same scale as other frustules. Measurements in 
microns of frustules from isolated atentacular 
hydranths (before any division of these fras- 
tules occurred) showed these variations: lengths 
575-375, mean 465; widths, thicker end 125— 
100, mean 106; widths, thinner end 100-75, 
mean 83. Figure 9B shows the size of this frus- 
tule drawn to the same scale. 
Although division was observed in frustules 
measuring 575-425 g, no division was observed 
in frustules measuring 375 g. The following five 
examples are typical of frustule lengths and the 
lengths of pieces into which they divided: 
LENGTH OF FRUSTULE 
O) 
LENGTH OF PIECES 
(/*) 
Short 
Long 
575 
150 
425 
500 
175 
325 
425 
175 
250 
400 
150 
250 
400 
150 
250 
The short pieces showed these variations 
(measurements in microns): lengths 175-150, 
mean 160; widths, thicker end 75-55, mean 65; 
widths, thinner end 50-37, mean 42. Figure 9 C 
shows the size of the small frustule fragment 
drawn to the same scale. 
The large pieces showed these variations 
(measurements in microns): lengths 425-250, 
mean 300; widths, thicker end 100—75, mean 
82; widths, thinner end 75-37, mean 54. Figure 
9 D shows the size of the large frustule fragment 
compared to sizes of other frustules. 
Buchert (I960 1 : 47) lists the following varia- 
tions for his Type A (atentacular) frustules 
(measurements in microns): lengths 6 35-441, 
mean 475; widths, thicker end 134-96, mean 
118; widths, thinner end 96-76, mean 88. 
Figure 9 'E shows the size of this frustule com- 
pared with sizes of other frustules. Although 
these data do not lend themselves to statistical 
analyses, they do suggest some interesting pos- 
sibilities. 
Frustule A is smaller than frustule B because 
