70 Miscellaneous. 
These two views are fundamentally different. Besides affecting 
our belief as to the manner in which bilateral symmetry arose, the 
acceptance of one or the other is the foundation of our understanding 
of the homologies which are to be found in the two groups. 
Evidence for the one or the other of the views is to be looked for 
in embryology ; but very few animals give an opportunity for such 
research, owing to secondary changes which have acted upon the ova 
and the embryos. For this reason no direct evidence has been 
hitherto obtained. At Beaufort, during the last summer, some work 
was done upon Thalassema, a species of worm which possesses a 
very primitive development, and enables a direct study of the origin 
of bilateral symmetry from radial symmetry to be made. The re- 
sults of the observations were satisfactory upon the point in ques- 
tion, and showed that, as far as this group of animals is concerned, 
the second of the above views, viz. that of Balfour, is in all essential 
respects correct. The radially symmetrical gastrula elongates nearly 
at right angles to its long axis, and gives rise to a bilateral larva, of 
which the ventral surface has been from the first indicated by the 
position of the mouth. The acquisition of a direct motion occurs 
some time after the animal is truly bilateral, an indirect revolu- 
tionary motion being gradually changed into a direct motion with its 
anterior extremity in advance.—Johns Hopkins University Cureu- 
lars, April 1888, p. 73. 
Observations on Blastogenesis and Alternation of Generations in the 
Salpe and Pyrosomata. By M. L. Joxrer. 
In 1868 Kowalevsky traced with precision the principal features 
of the blastogenetic development of the Salpe. According to him 
the stolon consists, as in the Pyrosomata, of two tubes, one within 
the other, prolonging the ectoderm and endoderm of the parent. 
In the free space left between them run four cords—two lateral, 
derived from the cloaca, two median (one inferior, the other supe- 
rior), derived from two masses of mesodermic cells. According to 
the same author the skin, the branchio-intestinal tube, and the 
cloaca of each of the aggregated Salpe are derived from the corre- 
sponding parts of the stolon, and, consequently, of the parent; the 
nervous system and the genital organs, formed at the expense of the 
median cords, result from the development of two groups of meso- 
dermic cells. 
Since this very precise exposition three chief memoirs have 
appeared upon the same subject; these have again brought into 
question the whole problem of gemmation and alternation of gene- 
rations. . 
Thus, according to Salensky, the inner tube as well as the lateral 
cords have only a transitory function: the latter are derived from 
the pericardium ; and the intestine is formed at the expense of the 
inferior cord. 
