ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 137 



and there is a power of bipedal progression, e.g. in Chiromeles ; (b) the 

 adaptation to suspension is in the callosities or an adhesive disk on 

 the plantar surface, e.g. Thyropoda and Myxopocla ; (c) the points of the 

 claws adhere to roughnesses on the rocks, e.g. Carollia ; and (d) the 

 suspension is effected by the long curved claws which grip the branches 

 like hooks. 



1NVERTEBRATA. 



Mollusca. 



Fresh-water Molluscs of Celebes. *— G. Bollinger makes a report 

 on a collection of molluscs — mostly of small size — from Lindu-lake in 

 Central Celebes. He records thirteen species, of which four are new, 

 Bythinia sarasinorum, Isidora badse, Planorbis sarasinorum, and P. badse. 

 There is also Isidora sarasinorum sp. n. from the south-east of the island. 

 A consideration of the collection points to the conclusion that the 

 molluscs of the basin in question have been derived from all sides and 

 represent a markedly mixed fauna. 



y. Gastropoda. 



Development of Periwinkle.! — H. C. Delsman gives an account of 

 the development of Littorina obtusata, one of the common periwinkles. 

 The eggs are laid in clumps on the fronds of Fucus serratus, and the 

 development lasts (in September) for fully three weeks. The diameter 

 of the unfertilized ovum is about 205 fx ; two maturation divisions 

 occur and after their completion two approximately similar nuclei are 

 seen in the egg. The first cleavage results in two equal cells, and the 

 second likewise. The third cleavage is unequal and " dexiotropic " (as 

 is the rule in Gasteropods with right-handed spiral shells) ; four macro- 

 meres (endodermic) are separated from four micromeres. The next 

 establishes the primary trochoblasts or " turret-cells " ; the next the third 

 quartette ; the next the mesentoblasts ; and so on. In the 49-cell 

 stage there are 7 endomeres, 2 mesentoblasts, and 40 ectomeres, but it 

 is difficult to picture their relations without the diagrams. The end of 

 the segmentation is a disk-like plakula of about 150 cells, the endomeres 

 being flattened out. Perhaps this should be regarded as the first step 

 in the gastrulation, which is very suggestive of that of lancelets. 



After the completion of the gastrula there is a remarkable change of 

 form, and the development of the veliger begins. The shell-gland is 

 seen very early, but there is no trace of the head vesicle which has been 

 observed in Fusus, Nassa, Crepidida, Calyptrsea, etc., and has a respira- 

 tory function. Perhaps the fact that the eggs are fastened to seaweed 

 in the surf -zone may explain the absence of any special respiratory 

 provision at this stage. There is no podocyst or yolk-mass, and the 

 structure of the veliger, with its foot, velum, stomodamm, and so on, is 



* Rev. Suisse Zool., xxii. (1914) pp. 557-79 (1 pi.). 



t Tijdschr. Nederland. Dierk. Ver., xiii. (1914) pp. 170-340 (10 pis.). 



April 21st, 1915 l 



