466 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Chordata, Salensky comes to the important conclusions that the sensory 
vesicle is homologous with the epiphysis and the Ascidian eye with the 
parietal eye. 
Origin of Organs of Salpa.* — Prof. W. K. Brooks has published an 
abstract of one of the chapters of his forthcoming memoir on the genus 
Salpa. He remarks that “ stated in a word the most remarkable peculi- 
arity of the $aZpa-embryo is this: it is blocked out in follicle cells 
which form layers and undergo other changes, which result in an outline 
or model of all the general features in the organization of the embryo. 
While this process is going on the development of the blastomeres is 
retarded, so that they are carried into their final positions in the embryo 
while still in a very rudimentary condition. Finally, when they have 
reached the places which they are to occupy, they undergo rapid multi- 
plication and growth, and build up the tissues of the body directly, 
while the scaffolding of follicle cells is torn down and used up as food 
for the true embryonic cells.” 
With regard to the aggregated Salpse , which during development 
undergo complicated changes of position, Salensky and Seeliger are 
said to have totally failed to understand the changes. The author now 
amplifies and expands the statement made by him some years ago, that 
the Salpa - chain is, morphologically, a single row of Salpse , all in the 
same position, with their dorsal surfaces proximal and their right sides 
on the right of the stolon. 
With regard to the ectoderm of the embryo, Salensky would again 
appear to have misunderstood the facts ; Prof. Brooks finds that it is 
derived from the extra-follicular blastomeres, and that the epithelial 
capsule is a transitory structure which is lost as the ectoderm re- 
places it. 
The caudal nervous system is represented by scattered blastomeres, 
which soon degenerate and disappear. The ganglion is formed as an 
invaginated fold of the somatic layer of the follicle, and the ganglionic 
blastomeres pass with it from the ectodermal ridge, and become com- 
pletely folded in among the follicle cells. The nerve- tube of the stolon 
is formed from the ectoderm in the middle line of the upper surface of 
the stolon. In the aggregated Salpse the nerve-tube arises as a solid 
rod, but it soon acquires a lumen ; as the ectodermal folds grow inwards 
and mark out the bodies of the Salpse , they cut the tube up into a series 
of ganglionic vesicles, one for each Salpa. The apparent migration of 
the ganglion is the result of secondary changes in the position of the 
bodies of the Salpse , and is not due to any change in the relation of the 
ganglion to other organs of the body. 
The history of the perithoracic tubes and of the atrium cannot be 
described intelligibly without figures ; the author finds that they are 
formed before the cavity of the pharynx is hollowed out in the mass of 
visceral follicle cells, and he shows that Salensky mistook them for the 
primitive digestive cavity.” In the aggregated forms the rudiment of 
each contains two perithoracic vesicles, derived from the right and left 
perithoracic tubes of the stolon ; their vesicles give rise to the peritho- 
racic system, and to nothing else. Throughout its whole history this 
* John Hopkins Univ. Circ., xii. (1893) pp. 93-7. 
