170 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
as in the Trematoda, precocious fission is not characteristic of the whole 
group, but occurs sporadically. 
The examination of other cases seems to indicate that some of the 
abnormal points in the development of Crisia may be due to the nutritive 
conditions in which the development takes place. Just as the presence 
of food-yolk within the egg modifies the character of the segmentation 
and germ-layer-formation, so the presence of copious stores of nutrient 
material in the maternal tissues outside the egg may affect the early 
processes of development. For example, the large number of relatively 
large larvae which develope from the minute egg of a Crisia could 
not be produced if the egg were not supplied with nutriment from out- 
side itself. On the other hand, the extreme independence of the blasto- 
meres at an early stage may be connected with the acquirement by the 
embryo of a habit of forming buds in the embryonic condition. 
General History of Marine Polyzoa.* * * § — The Rev. T. Hincks pub- 
lishes another part of his ‘ Appendix ’ ; certain modifications are proposed 
in the genus Steganoporella and its allies ; doubt is thrown on the dis- 
tinctness of the genus Stirparia ; there is a detailed discussion of the 
characters of Farcimia appendiculata ; there are remarks on various 
other species, and some answers to criticisms. 
Statoblast of Phylactolsemata.j — Dr. P. Demade, from a study of 
the statoblast in Alcyonella fungosa and Cristatella mucedo comes to the 
conclusion that the statoblastic mass is a tissue, and its membrane is 
composed of cells which undergo a cellular differentiation. 
Arthropoda. 
Parthenogenesis.^ — Prof. 0. Taschenberg has an interesting his- 
torical survey of parthenogenesis, accompanied by a very full biblio- 
graphy. It is almost half a century since the theory was first 
started, and it has succeeded in the important work of showing us that 
fertilization is not a necessary preliminary to the development of the 
animal egg. 
Compound Eye of Arthropods.§ — M. H. Viallanes has a contri- 
bution to this much discussed question. In his summary of the mor- 
phology of the eye of Palinurus vulgaris he describes the ommatidium 
as consisting of (1) a cornea, (2) corneagenous cells, two in number, 
and applied to the inner face of the cornea, (3) four crystalline cells, 
which appear to secrete (4) a cone. This cone is always formed of four 
segments, and in it there can be distinguished three regions — the crys- 
talline, the vitreous and the filamentar. The filaments are attached to 
the basal membrane. The next constituent, or retinula, is formed by 
the rhabdom and the seven cells which surround it. In the fresh state 
the rhabdom is coloured rose by chromatopsine ; it is a fusiform body 
with seven salient costae, which are the rhabdomeres. The retinular 
cells contain a quantity of pigment in their inner part, but none in the 
outer ; they are separated from one another by masses of pigment 
* Ann. and Mag. Nat. Hist., xi. (1893) pp. 175-82. 
t La Cellule (1892) viii. pp. 347-78 (2 pis.). 
+ Abhandl. Naturf. Ges. Halle, xvii. (1892) pp. 367-453. 
§ Ann. Sci. Nat., xiii. (1892) pp. 349-84 (2 pis.). 
