724 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
serrations at the mouth of the shell forms a prominent tooth-like process; 
and that this often looks worn, when the adjoining processes are intact. 
He one day saw one example of this species devouring a large Area, and 
noticed that the tooth in question held apart the valves of the Lamelli- 
branch aud prevented them closing; the Mur ex was thus able to insert 
its proboscis and devour the unfortunate bivalve. The Area ( Anadora 
pilosa ) is very difficult to detect, and shuts itself up at the least alarm. 
Development of Paludina.* — Herr R. v. Erlanger has studied 
the development of Paludina vivipara with special reference to the 
development of the pericardium, the heart, and the persistent nepliri- 
dium. In the youug gastrula there are no hints of primitive meso- 
blasts ; the mesoderm has its beginning in a ventral diverticulum of 
the archenteron. The ccelomic sac thus formed subsequently surrounds 
the gut in a bilaterally symmetrical crescent- shaped fold. Finally the 
mesoderm breaks up into spindle-shaped cells, which cross the body- 
cavity irregularly, but line the ectoderm on the one hand and the gut 
on the other. Erlanger believes that the mesoderm of Gastropoda 
is typically derived from the endoderm, in enterocoelic fashion, and 
thinks that the ova of the primitive forms had probably little or no 
yolk. A posterior aggregation of mesoderm cells, usually paired to 
begin with, represents the incipient pericardium ; the septum between 
its two divisions is soon ruptured and absorbed. An evaginate 
thickening of the right side of the pericardium represents the begin- 
ning of the permanent nephridium. The development of the secreting 
portion of the kidney from coelomic epithelium justifies the homology 
between the nephridia of Molluscs and of Annelids. On the left side 
there is a diverticulum which makes no progress ; it represents the rudi- 
mentary left nephridium. The heart appears as an invaginate groove 
on the dorsal wall of the pericardium. This groove is somewhat 
curved, and is at an early stage slightly constricted in the middle. It 
gradually becomes a tube, retaining an anterior and posterior communi- 
cation with the secondary coelom. The median constriction is the 
first hint of the division into auricle and ventricle. The author also 
describes the pair of primitive nephridia which lie to the right and 
left behind and below the velum. The occurrence of primitive and 
permanent nephridia suggests that the Molluscs have developmentally 
two segments. 
The Genus Atopos. j" — Dr. H. Simroth describes the structure of 
this new genus of Yaginulidae. He has studied three (all new) 
species : — Atopos Semperi , A. Leuekarti , and A. Strubelli. The internal 
anatomy is very peculiar. The heart, kidney, and lung are even 
further forward than in Limax , a position so divergent from that in 
Vaginula that Semper sought to refer Atopos to the Limacidae. The 
mouth has no jaw-plate ; the radula-sheath is remarkably developed 
and hidden in a special sac ; the sharp rapacious teeth suggest those 
of Testacellidae. From the mouth a pharynx leads to a short and 
narrow intestine, with a single but very large mid-gut gland in which 
the digestion takes place. The foot-gland is free, and around its 
* Morphol. Jahrb., xvii. (1891) pp. 337-79 (4 pis.). 
t Zeitschr. f. Wise. Zoo!., lii. (1891) pp. 593-616 (1 pi.). 
