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PEOGEESS OF MICEOSCOPICAL SCIENCE. 
The Sponges of the Channel. Their Development. — M. Charles 
Barrois has just published his valuable Thesis for the French degree 
of Dr. es Sciences Naturelles. It is dated July 1876. The follow- 
ing are the conclusions which the author has drawn. The author's 
observations were conducted with the view of making clearer the 
development of those sponges which belong to the most distinct group 
of the entire class. What the author has seen in the development 
of the sponges has led him to the conclusion that all the different 
groups present the same essential processes of development, but that 
the stages of development appear in a different order and more 
or less modified by various circumstances in the several groups. 
The general mode of development that he believes he is able to 
set forth from his observations seems to be not a Gastrula fixee en 
Hydraire, and the endoderm of which ramifies in the gastro-intestinal 
system ; but a compact mass composed of two superimposed leaflets, 
the external of which represents the exoderm, the internal stands for 
the union of the internal and median leaflets. This is, according 
to the author, the common form in the different species of sj)onges. 
The egg of the sponge a]^pears in the formative layer of the skeleton 
— the mesoderm of F. E. Schultze. It presents at first the same 
characters in the whole group ; but soon the formation of pigment and 
of pseudo-cells distinguishes the silicious sponges from the others. 
The author has never been able to see the process of fecundation. 
The segmentation is entire and regular ; each group presents pecu- 
liarities in the progress of this phenomenon, but nevertheless the 
result of it is constant; it produces a cavity of segmentation and 
finally a generally hollow sphere. This sphere differentiates itself into 
two distinct parts in all sponges ; the elements which will form the 
exoderm appear at one pole, and those which will form the other 
leaflets appear at the opposite pole. These processes present interest- 
ing peculiarities ; thus, whilst the distinction is recognizable in 
the calcareous and fibrous sponges in the early periods of segmenta- 
tion, it is not apparent in Halisarca and Halichondrida until the 
embryo arrives at the state of free larva. When the sphere is thus 
differentiated into two distinct histological halves, it produces in the 
CalcispongicB an invagination of one of these halves into that which 
represents the exoderm ; this is but a transition stage that he has not 
seen in the other families of sponges. Then follows devagination of 
the Gastrula of calcareous sponges; the limit between the two halves 
of the sphere thus produced corresponds to the former so-called 
mouth of the Gastrula. This part is clearly distinct in the free 
larvae of various families of sponges ; it is represented by a regular 
crown of cells in the calcareous sponges, by a crown of large flagella 
in the fibrous and silicious sponges, but it is less distinct in the 
larv£e of Halisarca. This crown is the starting point in the formation 
of the spicules ; it is the sole representative of the mesoderm of the 
