ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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probable that the epithelium of the radial glands converts the peptones 
into a soluble albumen which passes into the blood. Here the albumen 
would be taken up by amoebocytes and conveyed to various parts of the 
body. 
Development of Echinocyamus pnsillus.* — Dr. H. Theel has an 
important memoir on the development of this small Echinoid. After 
treating of 
(1) The ovum, its maturation and impregnation, the segmentation of 
the ovum (2) is considered, and here attention is chiefly given to the 
external characters noted with the living egg ; it was found that, in 
general, the rapidity of segmentation is proportional to the size of the 
segments ; at the first three cleavages the blastomeres are separated 
almost simultaneously, but afterwards some sets of segments divide 
earlier than others ; in the three first stages the blastomeres are equal 
among themselves, but afterwards they become distinctly unequal. 
The blastula (3) is elongate and cylindrical, and is peculiar for the 
early formation of calcareous spicules, inasmuch as in other Echinoids 
they do not appear till some later stage. 
It is at this stage too that, in Echinocyamus , a cell-area becomes 
differentiated at the animal pole ; it has a tuft of long cilia and probably 
serves as a larval organ of sense. 
(4) The gastrula of Echinocyamus appears to be remarkable for its 
length ; in most Echinoids the gastrulas are spherical or slightly^oval. 
Especial attention was (5) paid to the formation of the mesenchyme, as 
such different opinions have been held as to its origin. The conclusions 
to which Dr. Theel arrives are as follows : — 
(i.) With very few exceptions, the mesenchyme originates from the 
endoderm alone, and by means of immigration ; it will probably be 
found that the formation of this layer in many Echinoderms goes on 
uninterruptedly during the whole gastrulation. 
(ii.) The mesenchyme arises earliest, with very few exceptions, in 
those groups of Echinoderms in which the larvae have the skeleton 
earliest developed ; most of its earliest cells are calciferous. 
(iii.) No bilaterally arranged archi-mesenchyme cells are to be 
detected. 
(iv.) No true mesenchyme-bands, homologous with the mesodermic 
bands of Annelids or Molluscs, are met with in Echinoderms, but often, 
especially in Echinoids, the first wandering cells which enter arrange 
themselves in two bilateral heaps or bands. 
(6) The process of calcification appears to be effected by the calci- 
ferous cells supplying themselves with calcareous matter in such abund- 
ance that a part becomes solidified in the shape of reserve-granules, 
while the rest remain fluid. When the formation of a deposit is about 
to begin the calciferous cells combine by means of their clear pseudo- 
podial peripheral protoplasm protruding and combining together; this 
“ pseudopodial clump ” forms the organic ground-substance in which the 
calcification takes place ; during the act of solidification the resulting 
calcareous body assumes by degrees the shape of a tetrahedron, which 
gradually changes into a small three-armed star. Further increase is 
* Nova Acta Roy. Soc. XJpsala, xv. 1 (18^2) VI. 57 pp. (9 pis.). 
