206 THE AMERICAN NATURALIST. [VOL. XXXII. 
Cleavage was traced to thirty-two cells, which remain broadly 
united to one another at the centre of the whole mass. ‘The extra- 
ordinary conclusion is reached that, some of the deeply staining 
(“ chromatic ”) bodies of the outer zone of the egg form, during its 
first cleavage, nuclei, which have, however, no further rôle. 
Gastrulation and mesoderm-formation, long misunderstood, are 
cleared up. In the 32-cell stage, four cells enter the blastula cavity 
at the upper pole; they represent the entoderm. This degenerates, 
and a pseudo-blastula results. An ingression of cells at the upper 
pole of the now much larger embryo follows: this is the mesoderm- 
formation. ‘Thus the primitive entoderm is wholly rudimentary. 
The pair of primitive polypides also arise at the upper pole and the 
larva is soon thereafter born. The position of the primary polypides 
seems reversed in Gymnolæmata and Endoprocta as compared with 
Phylactolamata, for in the former groups this polypide arises at the 
pole at which gastrulation occurs. 
In regard to the /aw of seguence of buds, Braem insists on the wide 
difference between the budding of Phylactolemata and Gymnolæ- 
mata, since new polypides arise on the oral side of the old ones in 
the former, and on the anal side in the latter group. He forgets, 
however, that in both groups the anal side of the young bud is turned 
towards the source of its tissue. 
The work before us is destined to become a classic. The typog- 
raphy is of the best. Eight quarto plates, by Werner and Winter, 
contain drawings which, while trustworthy, are almost diagrammatic- 
ally clear. 
Lepidosiren. — From Natural Science we learn some facts regard- 
ing the development of the dipnoan, Lepidosiren, of Paraguay. Mr. J. 
Graham Kerr, of Cambridge, aided by a grant from the Balfour fund, 
went to Paraguay to obtain material for a history of this animal, and 
apparently was very successful in his search. Lepidosiren occurs in 
considerable numbers in the swamps, is rather sluggish, and comes 
to the surface at short intervals for respiration. Its food consists of 
the large snail, Ampullaria, and of confervoid alge, the young being 
more vegetarian in their diet than are the adults. The animal makes 
a burrow in the ground at the bottom of the swamp, lines it with 
soft grass, and in it deposits her eggs. These eggs are very large, 
about 7 mm. in diameter, and, in the developing eggs, have a thin 
and horny coat, derived from a gelatinous coat which surrounds the 
eggs before oviposition. The segmentation is holoblastic and 
