A NEW FIELD FOR THE MICROSCOPIST. 
127 
bably more original discovery waiting to be achieved than in 
any other group of the organic world. The forty or more specific 
types of the independent collar-bearing forms that have rewarded 
the writer’s desultory investigations spread over some five or six 
brief years, may be safely accepted as representing but a very 
small instalment of the innumerable varieties that are doubtless 
awaiting a more thorough and systematic research ; while of 
the sponges it may be said that we are as yet but imperfectly 
acquainted with the complete structural and developmental 
phenomena of even half a dozen out of the many hundred dis- 
covered species. In reference to these last-named organisms it 
is worthy of remark, before taking leave of them, that Pro- 
fessor H. James Clark, when first pointing out the intimate 
relationship between their essential living units and the two 
or three independent collar-bearing forms discovered by him- 
self, hazarded the opinion that future investigation would pro- 
bably reveal that different groups of sponges were composed 
of monads, corresponding in individual structure or presenting 
combinations of the various independent generic types ; and this 
anticipation has been remarkably fulfilled in the case of one 
of the simplest known sponge forms recently discovered, and to 
which the name of Gastrophysema primordialis has been given 
by Professor Haeckel. A small fragment of this interesting 
variety with its characteristic internal lining of collar-bearing 
monads is shown at Plate III. fig. 38, and this type may be said 
to present an amalgamation of the generic characters of the two 
genera Codosiga and Salpingoeca , certain of the monads being 
naked as in the former genus, and others enclosed within a, flask- 
shaped lorica, as in the latter one. In the last-named instance 
the monad illustrated has entered into a quiescent or encysted 
condition within its lorica, presenting under such circumstances 
an aspect absolutely identical with the similar encysted condition 
of Salpingoeca amphoridium shown at Plate IV. fig. 7. Pro- 
fessor Haeckel, unaided by an acquaintance with the independent 
collar-bearing forms here described and illustrated, and assum- 
ing for all sponges a coelenterate type of organisation, has 
singularly associated with these flask- shaped loricae and their 
encysted contents the structure and functions of rudimentary 
glandular organs. 
Before leaving the microscopist to make his first essay in that 
new and fertile field for investigation to which his attention is 
now directed, a few hints as to the conditions under which the 
most complete success is likely to be achieved may prove accept- 
able. The first matter of importance is his apparatus ; and here, 
should he not be in a position to command one of the highly 
perfected achromatic object glasses of our best English makers, 
let him be by no means discomfited. A German one-sixteenth 
