210 SUMMARY OF CURRENT RESEARCHES RELATING TO 



escape. A brief description is given. It is probable that they discharge 

 the ova and die soon after liberation from the colony. Hickson corrects 

 his previous description of certain cells in the ccenosarc of Millepora 

 as ova ; they ultimately give rise to the large kind of nematocyst. 



Ancestry of Helioporidae. * — Dr. J. W. Gregory suggests that 

 Heliopora, the recent blue coral, has descended from the palaeozoic 

 Heliolitidpe by degeneration in size and increase in number of the 

 ccenenchymal caeca, thus reviving the old view of the close affinity of 

 Heliopora and Heliolites which F. Bernard and Lindstrom have denied. 

 According to the author they are linked by a series of eocene and 

 cretaceous corals, among which is the genus Polytremacis. 



Regeneration in Gonionemus vertens.f — Prof. T. H. Morgan begins 

 a notice of his recent experiments on this Hydromedusa with a reference 

 to what Haeckel stated in 1870, | in regard to the regenerative capacity 

 of some of the Thaumantidffi ; — that if a medusa be cut up into more than 

 a hundred pieces, each piece, provided it contains a part of the margin 

 of the bell, will develope a complete little medusa. In 1897, C. W. Har- 

 gitt § noted that pieces of Gonionemus as small as one-fourth of the 

 whole have a remarkable recuperative power leading to the production 

 of the bell-like form, but he left it undecided whether these bell-like 

 individuals would produce the missing organs if kept for a longer time. 

 Morgan's experiments show that, although pieces somewhat smaller than 

 one-eighth of the medusa may make new individuals having the medusa- 

 form, yet these small individuals, as well as larger ones, lack the most 

 essential features of the medusa. The remodelling extends only to 

 the form of the entire piece, and does not include the internal organs. 



Morgan is inclined to believe that there is something more in the 

 remodelling than the fusion of the cut edges, and that the piece does in 

 reality mould itself into the medusa-form, as Hargitt said. The entire 

 process seems to be one of rounding-up of the piece in the direction of 

 least resistance, but it is a complex process in which several factors take 

 part. To try to analyse these is of more moment than to try to explain 

 the regeneration by a theory of preformed imaginary " germs " set aside 

 to bring about the result. 



Protozoa. 



Cyst-formation in Protozoa.]] — Herr Prowazek distinguishes three 

 kinds of cyst: — (1) protective cysts, which enable the organism to 

 withstand adverse conditions ; (2) reproductive cysts, which protect the 

 organism during the preliminary phases of multiplication ; and (3) 

 digestion cysts, induced by the superabundant ingestion of food. On 

 account of the ease with which they are distributed, these cysts often 

 occur in microscopic preparations of fresh material, especially of plants, 

 and thus may constitute puzzling objects. The author then figures and 

 describes the cysts of many of the common Protozoa. He adds to his 

 paper a note on the macrogonidia of a marine Zoothamnium which 

 appeared in an aquarium. The macrogonidia — the bulbi of Ehrenberg 



* Proc. Rov. Soc. lxvi. (1900) p. 19. 



+ Amer. Nat., xxxiii. (1899) pp. 939-51 (12 figs.). 



X Biologische Studien. Heft 1, 1870, p. 23. S Zoo!. Bulletin, i. (1897). 



|| Zeitachr. angevv. Mikr., v. (190(1) pp. 269-76 (1 pi.). 



