454 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Heliozoa. The remarkable “ corps en spiral ” which Fol is inclined to 
regard as a spermatophore appears rather to be a parasitic intruder, and 
is probably a life-stage in the history of one of the Orthonectida. 
Biological Results of Cruise of the ‘ Argo.’* — Prof. W. A. Herdman 
has a report on the biological results of the cruise of Mr. A. Holt’s steam 
yacht ‘ Argo ’ round the west coast of Ireland ; bad weather unfortunately 
prevented dredging in deep waters. Molgula holtiana and Polycarpa 
argoensis were two new Tunicates that were found during the expedition. 
Mollusca. 
j3. Pteropoda. 
Development of Clione limacina.t — Mr. N. Knipowitsch has a 
preliminary account of the development of this Pteropod, on which 
Fol has already made some observations. The formation of the 
gastrula commences with the division of one of four macromeres into 
two ; henceforward these two blastomeres distinguish the hinder end 
of the egg and are placed quite symmetrically ; the structure of their 
protoplasm, which is clearer, is not inconsiderably different from that 
of other macromeres. These cells are the mother-cells of the meso- 
derm. By the division and invagination of the three other macromeres 
a bilaterally symmetrical gastrula is developed. The blastopore is 
elongated and almost cleft-like ; it becomes gradually narrowed by the 
small ectodermal cells at its margin. 
After the formation of the gastrula the mesoblasts begin to develope 
and small mesoderm-cells with a coarsely granular protoplasm like that 
of the mesoblasts become formed. As the cells grow forward they 
arrange themselves in such a way as to form a splanchnic and a somatic 
layer. The cells of the endoderm pass directly into those of the mid- 
gut, and the only differentiation to be noted is that some of the cells remain 
rich in yolk while others are smaller and consist only of protoplasm. 
The former appear to become the hepatic cells. There seems to be 
no doubt that in those Pteropods where one macromere is smaller and 
poorer in nutrient yolk that cell gives rise to the mesoderm. 
y. Gastropoda. 
Embryology of Crepidula and TJrosalpinx.i — Mr. E. G. Conkton 
has a preliminary note on the embryology of Crepidula fornicata and 
Urosalpinx cinerea. In the former the cleavage follows the type of 
Fusus, Planorbis , Neritina , and others, but there is not, normally, any 
trace of an invagination at the ectodermal pole, such as has been 
seen in Neritina and Fulga. The gastrula is formed by typical epibole. 
The mesoblastic bands are soon separated from the mesoblasts, but the 
latter continue to proliferate mesoderm. The velum first appears on the 
ventral side and primitively consists of a single row of cells ; two large 
velar lobes become formed, one on each side. The velum does not 
become ciliated until quite late in development, though the embryo swims 
* Trans. Liverpool Biol. Soc., v. (1891) pp. 181-212 (3 pis.). 
t Biol. Centralbl., xi. (1891) pp. 300-3. 
X John Hopkins Univ. Circ., x. (1891) pp. 89-90. 
