162 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Effect of External Influences on Development.* — Prof. A. Weis- 
mann’s Eomanes lecture, of which we had a notice at the time of its 
delivery, f is now published in full, and fifteen notes, controversial and 
otherwise, have been added to it. 
Conception of Species.f — Mr. N. L. Britton discusses our conception 
of species as modified by the doctrine of evolution. He appears to think 
that species as we now understand them, whether recent or extinct, will 
gradually be invalidated, and he prophesies that our present methods 
of nomenclature will prove insufficient to meet the necessities of the 
new biological era which is so rapidly opening before us. 
Tunicata. 
Budding in Goodsiria and Perophora.§ — Dr. W. E. Bitter has a 
preliminary notice of his more important results in the study of 
G. dura sp. n. The bud is pallial as in the Botryllidae, and arises as 
an evagination of the wall of the peribranchial sac. Buds appear never 
to arise from fully adult ascidiozooids, and become entirely severed from 
the parent at a very early stage of development, i. e. before there is any 
trace of differentiation of organs. There exist in the common testicular 
mass great numbers of much branched, anastomosing vessels which 
terminate in large ampullae. These vessels contain no partition such 
as exists in the stolo prolifer of some other Ascidians, and plays so 
important a part in the production of blastozooids. The development 
of the organs of the blastozooids is in general quite similar to that 
which takes place in Botryllus. It is noted, however, that the common 
neurohypophysial rudiment arises at an early stage as a wide evagina- 
tion from the dorsal portion of the so-called endoderm. The pericardial 
vesicle is present at an early stage in the development of the ascidio- 
zooid, but the author has not yet been able to determine its origin. The 
heart developes from the pericardial vesicle in the usual way. It is 
suggested that Goodsiria and Botryllus will be found to be more closely 
allied than has hitherto been supposed. With regard to Perophora the 
author finds that numerous errors have crept into the descriptions that 
have been given by previous writers. When the endoderm becomes 
differentiated into the branchial and two peribranchial sacs it does so in 
such a way that the developing blastozooid is connected with the double- 
walled partition of the stolon, not by the branchial sac, as has been 
hitherto supposed, but by the left peribranchial sac. This communica- 
tion is entirely severed at an early stage in the development of the 
bud, and the author claims to have established that in P. annectens and 
P. Listen there cannot be an epicardium corresponding to the structure 
so called in Clavelina. The common rudiment of the central nerve- 
ganglion and the dorsal tube is one of the very first organs to appear, 
and every step in the differentiation of this rudiment into nerve-ganglion 
and dorsal duct can be followed with great ease and clearness. It 
appears to be certain that this common rudiment does not arise from 
* London, 8vo, 1894, 69 pp. f See this Journal, 1894, p. 434. 
t Trans. New York Acad. Sci., xiii. (1894) pp. 132-5. 
§ Anat. Anzeig., x. (1895) pp. 364-8. 
