224 
POPULAR SCIENCE REVIEW. 
at Charles Island, one of the southernmost. The probability of fragments 
drifting from one island to the other is very small, owing to the considerable 
depth of water between them. 
The Development of the Ascidian like that of a Vertebrate Animal. — One of 
the best accounts of the development of ascidia that we have seen in 
English is that in the “ American Naturalist/' by Mr. A. S. Packard, 
Junr. Mr. Packard says — after going into the subject at length, and 
with the aid of various woodcuts — it will be seen that some highly 
important features, recalling vertebrate characteristics, have occurred at 
different periods in the life of the embryo ascidian. Kowalewsky remarks 
that (i the first indication of the germ, the direct passage of the segmenta- 
tion cells into the cells of the embryo, the formation of the segmentation 
cavity, the conversion of this cavity into the body cavity, and 
the formation of the digestive cavity through invagination — these 
are all occurrences which are common to many animals, and have been 
observed in Amphioxus, Sagitta, Phoronis, Echinus, &c. The first point of 
difference from other animals in the development of all vertebrates is seen 
in the formation of the dorsal ridges and their closing to form a nerve- 
canal. This mode of formation of the nervous system is characteristic of 
the vertebrates alone, except the ascidians. Another primary character 
allying the ascidians to the vertebrates, is the presence of a chorda dorsalis , 
first seen in the adult Appendicularia by J. Muller. This organ is regarded 
by Kowalewsky to be functionally, as well as genetically, identical with that 
of Amphioxus. This was a startling conclusion, and stimulated Professor 
Kupffer of Kiel to study the embryology of the ascidians anew. He did 
so, and the results this careful observer obtained led him to fully endorse 
the conclusions reached by Kowalewsky, particularly those regarding the 
unexpected relations of the ascidians to the vertebrates, and it would appear 
from the facts set forth by these eminent observers, as well as Metschnikoff, 
Ganin, Ussow and others, that the vertebrates have probably descended 
from some type of worm resembling larval ascidians more perhaps than any 
other vermin type, though it is to be remembered that certain tailed larval 
Distomse appear to possess an organ resembling a chorda dorsalis , and 
farther investigation on other types of worms may lead to discoveries 
throwing more light on this intricate subject of the ancestry of the 
vertebrates. At any rate, it is among the lower worms, if anywhere, that 
we are to look for the ancestors of the vertebrates, as the Ccelenterates, 
Echinoderms, the Mollusks, Crustacea and Insects, are too circumscribed 
and specialized groups to afford any but characters of analogy rather than 
affinity. 
The Early Stages of the American Lobster. — Mr. S. I. Smith, whose paper 
on this subject appeared in abstract in a number of “Silliman’s American 
Journal ” (1872), has now published the essay in full, accompanied by a series 
of plates, and has been good enough to forward us a copy. His paper is of 
considerable length, yet, from the circumstance that he was unable to study 
the different forms in their living state, none of the internal anatomy is 
given. Nevertheless, the memoir is of value and will repay perusal, 
although it extends over too much space to render an abstract possible. We 
may observe that the terms employed are those which are used by Milne 
Edwards, Latin being substituted for French. 
