Group of the “ Physemaria.” 9 
monads, Codosiga and Salpingeca, and those socially im- 
mersed, the sponges, in a sarcodic matrix. For convenience’ 
sake I have proposed to distinguish these two respective sec- 
tions or subclasses as the Discostomata Gymnozoida and 
Discostomata Sarcocrypta. 
While at first sight a sponge-body, or Sarcocryptal Disco- 
stomatous colony, appears to present an almost incomprehen- 
sibly complex type of organization, it will be found on close 
investigation, assisted by an intimate acquaintance with the 
Gymnozoidal Discostomatous group, to be reducible to three, 
or even less, very simple elements. The first and most 
essential of these is necessarily .represented by the collar- 
bearing monads, the second by the simple Ameba-like cell- 
elements or cytoblasts, and the third by the general investing 
sarcode or syncytium. ‘These three elements intelligently 
recognized, or even the first and last only, all remaining 
structural details are most easily comprehended. Regarding, 
in fact, the collar-bearing monads as the one essential element 
of the sponge to which all the other structures are subsidiary, 
the investing sarcode or syncytium may be described as fur- 
‘ nishing, in the first place, a gelatinous fulcrum or basis for 
the reception and support of the essential monads, and, in the 
second, a suitable nidus or matrix for the nurture and deve- 
lopment of their offspring or reproductive products. To this 
last-named category, indeed, may be referred the Ameba-like 
cytoblasts and all the remaining larger or lesser granular 
contents of the syncytium. This explanation of the sponge- 
structure is offered not as a crude theory, but as the result 
of direct personal investigation, in the course of which the 
development of what at first sight appeared as mere granular 
specks, first into Ameba-like bodies, and then onwards into 
the characteristic adult collar-bearmg monads, was actually 
witnessed by me, as also the reassumption by these adult 
monads of an amoeboid state, their coalescence or fusion with 
neighbouring individuals, and final breaking up into innume- 
rable germs or spores similar to those from which they origi- 
nally sprang. The whole life-cycle is in fact perfectly 
identical with what obtains among the gymnozoidal section — 
of the class and all other simple monad forms, with the single 
difference that the reproductive germs, instead of being dis- 
persed into the surrounding water, are retained by, and grow 
up within, the substance of the syncytium. 
Although the method of increase above recounted represents 
the normal process of development among the sponges, there 
are certain departures from this simple formula which require 
a special explanation. The most important of these, and one, 
