204 SUMMARY OF CURRENT RESEARCHES RELATING TO 



some special kind of enemy. If it be true that they are not found on 

 other species of the genus, we shall have another proof of their late 

 development in time ; their great size has prevented their develop- 

 ment in large numbers on the same person, and may be the explana- 

 tion of their asymmetrical character. No organ known in any other 

 Coelenterate can be compared with them, with the exception of the 

 nematophores of the Plumularida, in which there is a process con- 

 tinued from the endoderm, though one that is only feebly developed. 

 Three kinds of offensive organs seem, therefore, to have arisen inde- 

 pendently of one another, for in the Hydractinidae they are repre- 

 sented by the so-called spiral zooids. 



Siphonophora of the Bay of Naples.* — M. Bedot finds that the 

 Bay of Naples is one of the richest of all parts of the Mediterranean 

 for these interesting forms ; in one season he found 17 species, and 

 altogether he knows of 19 ; all the families of the order are repre- 

 sented, and Physophora pMlippii, ForsJcalia contorta, Halistemma 

 ruhrum, Praya diphjes, and Biphyes quadrivalvis are very abundant. 

 Of the last-named form the author had some specimens 60 cm. long, 

 and he once observed an abnormal example, with three swimming- 

 bells. 



Ctenophora of the Bay of Naples.f — A very complete abstract of 

 this monograph by the author, Dr. C. Chun, will be found at pp. 193-5, 

 and 212-26 of Part 1 of the ' Zoologischer Jahresbericht' for 1880. 



Protozoa. 



Sjnnbiosis of Lower Animals with Plants.— Yellow Cells of 

 Radiolarians and Ccelenterates. — See infra, Botany, Algse. 



New sub-class of Infusoria— (Pulsatoria).:J: — Three years ago 

 Mr. P. Geddes described § some curious cells which occur in large 

 numbers in the mesoderm of the Planarian Convoluta schulzii. The 

 cells are a little smaller than the red blood-corpuscles of the Frog, 

 are nearly in the form of a slightly curved pear, and have a large 

 central vacuole, filled with fluid. On the wall of this cavity, and 

 towards the more convex side of the cell, almost parallel with its 

 principal axis, there is a row of homogeneous and transparent fibrillee 

 which are inserted at their upper and lower extremities in the ordi- 

 nary protoplasm of which the other parts of the cell is composed. 

 This differentiation into a granular and fibrillar part is comparable 

 to that which takes place in the embryonal muscular cells of the 

 Tadpole, and recalls somewhat the structure described by Lankester 

 in the heart of Appendicularia. If these cells are examined 

 free in sea-water it is seen that they are in a state of rhythmical 

 contraction, the rapidity and vigour of which are equally surprising, 

 the most active pulsating from 100 to 180 times per minute; each 



* MT. Zool. Stat. Neapel, iii. (1881) pp. 121-3. 



t Fauna u. Flora des Golfes von Neapel, Mon. I. pp. xviii. and 313 (22 

 figs, and 18 pis.). 



X Coraptes RenduB, xciii. (1881) pp. 1085-7. 

 § Proc. Roy. Sec, xxviii. (1879) p. 449. 



