584 SUMMARY OP CURRENT RESEARCHES RELATING TO 



and they have been carefully edited by Mr. John Hopkinson. The 

 volume gives an historical introduction, an account of the structure and 

 relationships of the class, and a description of the species (30) of A&cidia. 



INVERTEBRATA. 



Mollusca. 

 a- Cephalopoda. 



Symbiosis of Hydractinian with a Cephalopod.* — F. Baron 

 Nopcsa describes from the Fayum district of Egypt specimens of the 

 Eocene genus Kcrunia, which Mayer- Eymar regarded as a Cephalopod, 

 and Oppenheim as a Hydractinian. His view is that Kerunia "resulted 

 from a remarkably close symbiosis of a Belosepia-like Cephalopod with 

 an encrusting Hydractinian, in which symbiosis went so far that the 

 Hydractinian overtook the labour of building up the primitive shell of 

 the Cephalopod which fixed or controlled to a certain extent the growth 

 of the Hydractinian." 



y- Gastropoda. 



Study of the Mud Snail.j — Abigail Camp Dimon has made a study 

 of the habits and reactions of Nassa obsoleta. On a dry substratum it 

 prefers shade to direct sunlight ; on a damp substratum in diffuse light 

 it moves towards the light. In an aquarium the mud-snails tend to 

 group themselves on the lighter side. The siphon and tentacles are 

 sensitive to sudden changes in the intensity of illumination. The 

 animal tends to move against a moderately strong current, and to rest 

 with its head against the current. It may live four or five days out of 

 water. It eats both animal and vegetable food, but prefers the former ; 

 it will not eat unless covered with water. Copulation occurs during the 

 rise of the tide, and is followed by the deposition of capsules, which 

 contain a variable number of eggs. A veliger hatches, which develops 

 in two weeks into a form like the adult. The mud-snail holds its place 

 because of its adaptability to varying conditions, and because no other 

 mollusc entirely competes with it. The only form with which Nassa 

 obsoleta is not at present adapted to compete is Littorina litorea, and 

 the struggle between them may result in a modification of the range of 

 the former. 



Development of Kidney and Heart in Planorbis.J — 0. Potzsch 

 has followed the history of the mesoderm in Planorbis cornea from one 

 of the macromeres onwards, and has traced the development of the 

 kidney, pericardium, and heart, which arise from a common rudiment. 



Kruppomenia and the Radulse of Solenogastres.§ — H. F. Nierstrass 

 gives an account of Kruppomenia minima, a new Solenogaster from deep 

 water in the Gulf of Naples. There is a thick cuticle ; the spicules are 

 like those of Proneomenia, in many layers ; a ventral fold extends to 

 the cloaca ; the radula is distichous ; there are two spherical salivary 



• Ann. Nat. Hist., xvi. (1905) pp. 95-102 (1 pi.). 

 + Cold Spring Harbor Monographs, v. (1905) pp. 1-4S (2 pis.). 

 t Zool. Jahrb.. xx. (1904) pp. 409-38 (3 pis. and 10 figs.). 

 § Op. cit., xxi. (1905) pp. 655-702 (3 pis. and 7 figs.). 



