164 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
cap consisting of a few irregularly arranged cells. In other cases the 
egg was further surrounded by a layer of flat epithelial cells, below 
which a few others of similar appearance were also to be seen. The 
appearance, contrasted with normal segmentation, suggested a pseudo- 
ectoderm and pseudo-mesoderm. In Murex brandarius similar abnor- 
malities occur in early stages. But in Cassidaria the abnormality may 
persist so that the dwarf embryos, resulting from the peculiar segmenta- 
tion, reach a veliger stage. The author directs the attention of those 
who work at experimental embryology to what he has described. 
Shell-Structure.* — Dr. J. Thiele begins with a description of the shell 
of Chiton. It has four layers, periostracum, tegmentum, articulamentum, 
and hypostracum. In Area, he describes periostracal glands which 
probably help in forming the periostracum, and notes how the glandular 
mantle epithelium, which is locally modified into attaching epithelium, 
forms an hypostracum distinct from the ostracum formed from the outer 
surface of the mantle-fold. The tegmentum of Chiton is an ostracum, 
the articulamentum has no equivalent among Lamellibranchs, the inner- 
most layer is an hypostracum. In almost all types the ostracum and 
hypostracum are distinguishable, and many illustrations are given. The 
ostracum is primary, traceable to the cuticula of Amphineura, and 
ontogenetically oldest; the hypostracum is secondary, and effects the 
attachment of the muscles to the shell. 
S. Lamellibrancliiata. 
Structure of Cuspidaria and System of Lamellibranchiata.j — 
Prof. C. Grobben describes Cuspidaria ( Nesera ) cuspidata Olivi, cor- 
roborating some of the results of Pelseneer’s recent work, but in regard 
to some points giving different descriptions and drawing different con- 
clusions. He describes a byssus-gland in the foot, the branchial septum 
with its complex musculature (almost wholly striated), its five pairs of 
clefts, and its mechanical function in causing water- currents in the 
mantle chamber, the gut (in regard to which he has little to add to 
Pelseneer’s account), the kidneys which lie behind the pericardium and 
in general characters are very like those of Najadsc, the entire absence 
of blood-vessels and their replacement by sinuses, the freedom of the 
rectum from the ventricle, the respiratory function wholly discharged 
by the mantle, and the nervous system (in regard to which Pelseneer’s 
account is almost completely confirmed). While Pelseneer described 
his C. rostrata as hermaphrodite, Grobben finds that C. cuspidata has 
separate sexes, and he gives reasons showing that Pelseneer must have 
been mistaken. The author agrees with Pelseneer’s union of Poromya , 
Silenia ( = Cetoconcha ), and Cuspidaria in a group of Septibranchiata, 
but he would not grant the group more than subordinal value. 
Phagocytosis in Gills of Lamellibrancliiata. :[ — M. de Bruyne states 
that, if we cut off a fragment of a gill of, preferably, a Mytilus, and 
examine it with Zeiss oc. 4 and obj. F (magnification 1010) an ex- 
amination can easily be made of the blood-corpuscles. At the edge of 
the epithelium a wandering corpuscle may be seen to leave the con- 
* Zeitschr. f. Wiss. Zool., lv. (1892) pp. 220-51 (1 pi., 1 fig.). 
f Arbeit. Zool. Inst. Univ. Wien (Claus), x. (1892) pp. 101-46 (4 pis.). 
i Comptes Rendus, cxvi. (1893) pp. 65-8. 
