Thraustotheca , a Peculiar Water-Mould. r 59 
and contraction or compression of the spores. At any rate, comparative 
measurements demonstrate that the sporangium has distinctly decreased in 
size. Since Rothert ( 24 ) in Saprolegnia saw the clefts extend and rupture 
the remaining peripheral layer of protoplasm, we may infer that in the 
present instance also this rupture has taken place, allowing the escape of 
cell-sap from the clefts with a consequent shrinkage of the sporangium and 
partial obliteration of the lacunae of demarcation between the spores. The 
translucent and vacuolate condition of the content is of brief duration, and 
there seems no need of regarding the vacuolation as marking a separate 
stage in sporangium development. 
In the final phase, which next ensues, the spores, now clearly granular 
and surrounded individually by delicate membranes, imbibe water and swell, 
becoming more and more separate (Fig. 10). It is to be noted that 
the sporangiospores have maintained their identity from the beginning of 
the process. As Figs. 6-13 show, the completed spores occupy the 
identical positions of the spore initials when first marked off by the clefts. 
There is, moreover, no evidence to support the assertion of Btisgen (6) and 
others that the spore initials fuse to a homogeneous mass. 
The foregoing description applies particularly to the densely filled 
sporangia; but in the less common axially vacuolate sporangia, as well as 
in certain abnormal sporangia (Fig. 38) which are characterized by large 
central vacuoles and thin peripheral protoplasm, and which develop at 
a temperature near the maximum (31-32° C.), spore-formation is also asso¬ 
ciated with the centrifugal extension of cleavage furrows. If, however, the 
sporangium wall is punctured just as cleavage begins, both the protoplasm 
that escapes and that which remains undergo division into irregular 
spore-masses by an incomplete cleavage from the surface inwards (Figs. 40 
and 41). 
It is to be noted that the process of sporangiospore formation in 
Thraustotheca presents no evidence of an intersporal substance, but agrees 
in the main with the descriptions of Rothert ( 24 ) and Humphrey ( 15 ) for 
other Saprolegniaceae. The assertion of de Bary (4) and of von Minden 
(21) that the sporangiospores of Thraustotheca are embedded in a ‘ Zwischen- 
substanz ’ is probably based on Busgen’s misinterpretation of the process 
of spore formation in the species, rather than on individual observation of 
living materials. 
Liberation of the Sporangiospores. The method of spore liberation in 
Thraustotheca differs from that which has been described for any other 
genus of the Saprolegniaceae. The papillae of dehiscence which charac¬ 
terize most members of the family are lacking, and the non-motile 
sporangiospores escape by bursting the sporangial wall. At high tempera¬ 
tures (30-31° C.) occasional sporangia develop apical papillae (Fig. 38) 
which closely resemble the normal escape papillae of other genera. In 
