52 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
which are formed sooner or later from the endoderm, these divide into 
prechordal and chordal (or caudal) portions, of which the former 
breaks into mesenchyme cells, while the latter forms only the tail 
muscles. 
(3) The peribranchial sacs and cloaca. — The peribranchial apparatus 
arises (a) from the peribranchial invaginations ; ( b ) from the branchial 
canals ; and (c) from the cloacal invagination. The author gives a 
useful comparative table of the state of each of these parts in the 
different types. 
(4) The respiratory and intestinal tract consists (1) of the branchial 
or pharyngeal sac, which, along with the peribranchial apparatus forms 
the clefts, and (2) of the intestinal canal which arises along with the 
former. In Tunicates there is really only one pair of true g ill-clefts ; 
the secondary clefts are not homologous with those of Vertebrates. 
(5) The branchial sacs, the procardium , the pericardium , and the 
heart. — The two branchial sacs of Didemnum represent procardial canals, 
the single branchial sac of Diplosoma is the right and the only pro- 
cardial canal. In Didemnum the procardial canals serve for the formation 
of pericardium and epicardial canals, but the single branchial sac of 
Diplosoma becomes the branchial sac of the ventral individual and has 
nothing to do with pericardium or epicardial tube which arise inde- 
pendently in each of the two individuals. The heart is a product of 
the pericardium, but in Appendicularia the so-called heart is a peri- 
cardium (the cellular membrane) with a but slightly developed heart- 
invagination (the muscular wall). 
(6) The notochord is then discussed, and this leads to an essay on 
the ancestry of Vertebrates. Salensky’s views are that the Proto- 
chord ate was worm-like, with a straight gut having paired metameric 
pouches and a terminal anus, and with a strand-like nervous system. 
Two factors operated in the differentiation of this type — the anterior 
pouches broke through and became branchial ; the posterior pouches 
coalesced and formed a supporting organ. There was probably a coelom 
arising from endodermic diverticula. 
(7) The cellulose mantle arises primarily from the kalymmocytes, 
but mesenchyme cells and processes of the ectoderm may help. 
Finally, in a third chapter Salensky describes the longitudinal-frontal 
division of the Diplosoma embryo which results in the dizoic larva. 
“ Sub-neural” Gland in Ascidians.* — Dr. M. M. Metcalf describes 
the neural gland of Botryllus Gouldii. The facts of special interest are 
(1) that the gland and its duct are dorsal to the ganglion (as also in 
Molgula Manhattensis , Cynthia partita, and Boltenia Bolteni ) ; (2) that 
there is no truly glandular portion ; and (8) that the posterior end of 
the gland is fused with the posterior end of the ganglion. 
Mollusca. 
y. Gastropoda. 
Development of Stylommatophora.t — Dr. F. Schmidt has studied 
early stages of Succinea, Limax, and Clausilia. His results chiefly con- 
cern the sensory plates, the foot, and the shell area. 
* Anat. Anzeig., xi. (1895) pp. 277-9 (3 figs.), 
f Zool. Jahrb., viii. (1895) pp. 318-41 (9 figs.). 
