672 The American Naturalist. : [July, 
of the cells of the two germ-layers, and is to be distinguished from the 
true invagination (embole) as pseudoembole. 
‘ The development of the compound Ascidians is easily distinguished 
from that of the social Ascidians. Here the plakula turns in by 
another process, since the gastrula-cavity (which formed the archente- 
ron in Clavellina) is filled in the dorso-ventral direction with dividing 
endodermal cells. Now the archenteron arises neither by embole or 
by pseudoembole but by delamination of the large endodermal cells 
(Distaplia amarecum). ‘The closing over of the endoderm by the 
ectoderm takes place in Distaplia by a different process in different 
parts of the embryo; anteriorly it is purely epibolic ; posteriorly, on 
the other hand, this takes place by a division of the dorsal endoderm 
cells (endodermplate), which at the same time, together with the ecto- 
derm cells in question, grows around a space (pseudogastrula-furrow), 
which space is later filled by the endodermal cells themselves. This 
process, taking place in the pseudoembolic region of the embryo, 
must be looked upon as a rudiment of embole, which, in spite of great 
changes in the egg of social Acidians, occurs in the typical way.” 
This series of stages, from the simple to the social, to the compound 
Ascidian, furnishes an excellent example of Hatschek’s law that ‘‘ by a 
phyletic change in a group of animals not only the adults (end stage) 
are changed, but also the whole series of embryonic stages, from the 
egg to the adult’ (end stage.) 
Rabl’s phylogenetic classification of the vertebrates according to 
the accumulation of yolk is criticised and objected to. We need not 
here enter into the detailed description of the origin of the mesoderm, 
the digestive tract, and the notochord, which occupies the last fifty 
pages of the paper. 
Development of the American Lobster.—Two preliminary 
papers, one on the habits and larval stages of the lobster, and the 
other on the reproductive organs and early stages of the lobster, have 
been published by Prof. F. H. Herrich.* ‘‘ The spawning season is con- 
fined to the summer months, and the eggs which are then laid are 
carried by the female throughout the fall, winter, and spring, and are 
not hatched under natural conditions until the following summer.’’ The 
number of eggs laid varies from about 3,000 to 36,000 ; a lobster 1034 
inches long produces on an average 12,000 eggs. The lobster does 
not breed annually. The eggs laid in summer develop with compara- 
tive rapidity, and eye pigment is formed in 27 to 30 days. Develop- 
ment slows up in the fall, and comes nearly to a standstill in the 
3 Johns Hopkins University Circular, No. 87, 1891. 

