ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
367 
many recent researches have made prominent, and which his own study 
of Ecteinascidia turbinata, one of the Clavelinidte, confirms. The bud- 
development of this form is very like that of Perophora annectens , though 
without the peculiar rotation or transverse shifting of the inner vesicle 
which occurs in the latter. The absence of an epicardium, with which 
the formation of the pericardium is closely connected, sharply contrasts 
these two genera with Glavelina. In Ecteinascidia and Perophora 
annectens the pericardium, dorsal tube, and ganglion (and in the former 
the gonads also), are all formed, in greater part at least, from cells which 
wander out from the wall of the inner vesicle into the rudiments. The 
primitive vesicle is the all-important part of the bud-rudiment, providing 
material for all the internal structures, for the ectoderm has no active 
role except as regards the test. Whether derived from an ectodermic 
or an endodermic larval structure, it gives rise to all the organs derived 
in embryonic development from the two primary germinal layers, and 
in some cases it also furnishes cells to the blood, as in the two forms 
last-mentioned. But although it is undifferentiated, like a blastula, it 
is mapped out into areas which form particular structures ; and it is 
possible to make a series showing varying degrees of this differentiation. 
Thus, at the lowest end stands Perophora viridis; a step higher we find 
Ecteinascidia and Peropliora annectens ; a still higher grade is illustrated 
by Botryllus and many others. 
Compound Larva of a Synascidian.*— M. Maurice Caullery has 
studied Diplosomoides Lacazii Giard, a Synascidian of the family Didem- 
niae, which, as Lahille has observed, begins to bud during the develop- 
ment of the oozo'id. According to Lahille, the hatched larva is already 
a colony of three individuals — the oozoid and two blastozoids. Accord- 
ing to Caullery, the hatched larva includes (a) the oozoid, typical, 
except that the terminal part of the digestive tube is atrophied ; (b) a 
typical abdominal bud ; and (c) two complementary thoracic half-buds. 
Perhaps it is most correct to say that there are two individuals— the 
oozoid and diverse parts of a blastozoid. It has a twofold interest, (1) in 
the precocity of the budding, and (2) in the separation of the two halves 
of the thoracic bud. The latter peculiarity may be explained by the 
presence of an abundant vitellus ; it may be an illustration of the 
mechanical influence of the vitellus on the processes of morphogenesis. 
Follicle-Cells in Salpa^ — Mr. M. M. Metcalf discusses these cells, 
which have been the subject of such discrepant interpretation. Salensky 
believed that the fertilised ovum merely served as food for its unfertilised 
sister-cells — the follicle-cells — which he regarded as truly formative. 
Brooks believed that the embryo was blocked out in follicle-cells, which 
were afterwards replaced by blastomeres. Heider and Korotneff have 
continued the inquiry. What Metcalf has shown may be very briefly 
stated. He finds that the disputed bodies within the blastomeres have 
a distinctly nuclear character, and he interprets them, with Brooks, but 
against Heider and Korotneff, as the ingested nuclei of the follicle-cells. 
Heider regarded the bodies as nucleated cells, Korotneff found no trace 
of a nucleus within them, Metcalf says they are nuclei in process of 
digestion. 
* Comptes Rendus, cxxv. (1897) pp. 54-7. 
f Zool. Anzeig., xx. (1897) pp. 210-17(1 fig.). 
1897 2 d 
