706 
SUMMAllY OF CURRENT RESEARCHES RELATING TO 
tarn itself about. The invaginate cups are not supplied by any nerves, 
and cannot be optic. 
In the Mytilaceae there are also two kinds of glands, muciferous and 
poisonous. The peculiar knob-like prominences on the mantle-margin 
of Pinna are certainly not eyes but glands, though they are very remark- 
able in being directly innervated. The characteristics of Mytilus, 
Modiola, and Lithodomus are described in detail. In Unionacese the 
mucin-forming glands alone are present. According to Flemming, the 
abundant mucous material of bivalves is secreted by the mucous cells in 
the meshes of the connective tissue, but Eawitz denies this to be the 
case in the Ostreacese, or in Area node , barbata , tetragona , lactea, Nucula 
nucleus , Mytilus edulis , Lithodomus dactylus, or Pinna nobilis , while he 
allows it tor Area diluvii , Pectunculus glycimeris , Modiola barbata, and 
the Unionacese. It is interesting, however, to notice that the product in 
Unionacese is different from that in the other three forms. Finally, 
Rawitz points out that the occurrence of amorphous secretions in the 
connective tissue seems a symptom of degeneration as seen for instance 
in Area diluvii , and that the younger species in a phylogenetic series 
show preponderant secretory activity and degenerate sensory structures. 
Molluscoida. 
a. Tunicata. 
Development of Pyrosoma.* — Prof. W. Salensky finds that the 
embryo of Pyrosoma arises from both fertilized and unfertilized elements, 
since the formation of the cyathozoid is due, not only to the blastomeres, 
but also to the “ kalymocytes,” as the author terms the “ internal folli- 
cular cells ” of Kowalewsky. The first differentiation of the germinal 
layers is seen in the separation of the cells into two strata, an ectoderm 
and a meso-entoderm, of which the latter is further differentiated into 
a many-layered mesoderm and a single-layered entoderm. The meso- 
derm appears in the form of two typical coelome pouches, but of these 
only the left developes. It is modified into axial mesoderm and a 
pericardial sac, while the right pouch breaks up into cells which are 
afterwards scattered in the body of the cyathozoid. 
£. Bryozoa. 
Gemmation of Bryozoa.f — Herr 0. Seeliger commences his memoir 
with an account of the development of the entoproctous Bryozoa, as 
illustrated by Loxosoma. The history is very similar to that of Pedicel - 
Una . Parts of the ectoderm and mesoderm give rise to buds, the endoderm 
of which is formed from the outer layer by a process comparable to that 
of gastrulation by emboly. From the basal portion of the invagination 
the digestive tract is formed, and from that which remains always in con- 
nection with the endoderm arises the atrium and the outer covering of the 
tentacles. On the other hand, there are certain differences ; the point at 
which the buds are formed is different, for in Loxosoma it is the body- 
wall of the upper part, and in Pedicellina the stalk. Again, the topo- 
graphical relations of the body-regions of the buds to those of the 
* Biol. Centralbl., x. (1890) pp. 225-33. 
f Zeitsohr. f. Wiss. Zool., 1. (1890) pp. 560-99 (2 pis.). 
