ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
163 
the ectoderm. What evidence there’ is as to its origin, points to its 
development from the free cells of the blood. 
Budding of Distaplia magnilarva.* * * § — Dr. J. Hjort and Herr F. 
Bonnevie find that the various stages of the budding of Distaplia are 
anatomically most like the buds of Botryllus and Polyclinum. The ner- 
vous system and hypophysis arise from the inner vesicle which is of 
endodermic origin. The outer vesicle is of no importance in the 
formation of the internal organs and only forms the integument of the 
adult bud. It follows therefore, that gemmation in Distaplia , as in 
Botryllus and Polyclinum , proceeds on essentially different lines to 
gemmation amongst other forms of animals. Regeneration, as much as 
larval development, is a process of new formation. The authors have not 
yet been able to decide the relation the bud of compound Ascidians bears 
to the bud of Pyrosoma and the Salpidse. They believe, however, that 
the same laws hold for the compound Ascidians as for the others. 
Supposed Vertebration of the Tail in Appendicularia.t — Mr. J. 
Rankin has investigated the tail of Oikopleura dioica and Fritillaria 
furcata, and finds it impossible to admit that its structure shows meta- 
meric segmentation. The axial chord is allowed by all to be unseg- 
mented ; the nerve-cord shows a very irregular distribution of ganglia ; 
the interruptions in the musculature are artificial fractures along trans- 
verse lines of weakness , but are remarkably constant in number, usually 
nine in 0. dioica. For these and other reasons the author denies the 
alleged vertebration. Recent investigations of the same subject by 
Lefevre and Seeliger are duly taken note of and criticized.^ 
Development of Salpa democratica.§ — Prof. A. Korotneff notes 
that three sets of elements are involved, (1) the blastomeres, (2) the 
gonoblasts or kalimmocytes, derivatives of follicular cells, probably to 
a very small degree formative, if at all ; and (3) what he proposes to call 
histogens which spring from blastomeres, and are intermediate between 
them and tissues. 
Around the fertilized ovum, there is (a) a follicular capsule, and 
(b) a “ brood-sac ” which arises from a duplicature or in sinking of the 
epithelium of the branchial cavity. The gonoblasts insinuate themselves 
among the blastomeres ; at the same time the cells of the lower layer of 
the “brood-sac ” form a loose mass in common with the gonoblasts; and 
in this the dividing blastomeres proliferate. 
The blastomeres collect in the centre and multiply ; their deriva- 
tives form “ histogens,” but some acquire large expanded nuclei and 
gradually degenerate into food-material. Some histogens multiply 
rapidly and form the mesenchyme — connective tissue and blood. 
The histogens accumulated in the centre make a passage into the 
cleft of the brood-sac and fill up the lumen, forming a continuous ecto- 
derm. After this is formed, the cells of the inner layer of the roof of the 
brood-sac separate from one another, and have the ectoderm covered only 
by the epithelial cells of the branchial cavity duplicature alluded to 
* Anat. Anzeig., x. (1895) pp. 889-94 (3 figs.). 
t Zool. Jahrb. (Abtli. Anat. Ontog.), viii. (1894) pp. 289-300 (1 pi.). 
X See this Journal, 1 894, p. 557. 
§ Biol. Centralbl., xiv. (1894) pp. 841-6 (6 figs.), 
M 2 
