162 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Coelentera. 



Variation and Regulation of Abnormalities in Hydra. * — H. H. 

 Parke finds that the number of tentacles in H. viridis varies from 4-11 ; 

 that the average number varies in specimens from different localities ; 

 that large specimens have more than the small specimens have, and old 

 forms more than young ones. 



The size of tbe just-separated bud is on an average directly pro- 

 portional to the size and number of tentacles in the parent ; the number 

 of tentacles in the just-separated bud is less than that in the parent ; 

 it varies between four and six, and is in direct relation to the size of the 

 bud and of the parent. 



The number of tentacles in an individual is not constant ; it may 

 increase during life, or it may decrease in unpropitious conditions. 

 There is less numerical variation in H. fusca than in H. viridis. Longi- 

 tudinal division sometimes occurs in Hydra. 



Porifera. 



Minute Structure of Sponge Spicules.^ — Prof. 0. Biitschli finds 

 that gentle heating reveals a fine vesicular or alveolar structure, which 

 is probably represented, though too fine to be seen, in the normal state 

 of the spicules. The axial thread of siliceous spicules gives albuminoid 

 reactions, and there is some organic matter along with the siliceous sub- 

 stance. The thread may be stained when there is some breakage in the 

 spicule, or when one end is still open. In Tethya the siliceous needle 

 is entirely surrounded by girdle-like cellular bands (silicoblasts), and 

 branched cell-like bodies are sometimes seen between the thread and the 

 wall of the axial canal. In Leucandra there is no axial thread, and only 

 the sparsest representation of organic substance. But we cannot give 

 more that an indication of the chief results of this elaborate study. 



Protozoa. 



Cell-Division in Protozoa.^ — Dr. F. Doflein has studied Noctiluca 

 miliaria with special reference to the nuclear changes accompanying cell- 

 division. He gives the life-cycle as follows: — The adult multiplies by 

 cell-division repeatedly and finally comes to rest, copulation of two in- 

 dividuals occurs, and is followed by rapid budding ; the liberated buds 

 are at first similar to Dinoflagellata, but ultimately become couverted 

 into adults. When division occurs a sphere appears near the nucleus, 

 and a process presenting what the author regards as a superficial re- 

 semblance to the karyokinesis of Metazoa follows. The actual process 

 of nuclear division seems to some degree independent of the division of 

 tbe sphere, but the latter is intimately associated with the division of 

 the plasma. This is explicable on the author's view that the sphere is 

 merely a concentration of the plasma. The budding after copulation 

 consists in rapid cell-division, during which the division products remain 

 connected by a common stroma. Whether this 6troma does or does not 

 indicate the existence of a process of reduction remains uncertain. The 



* Arch. Entwickmech., x. (1900) pp. 692-710 (9 figs.). 



f Zeitschr. wiss. Zool., Jxix. (1901) pp. 235-86 (3 pis. and 2 figs.). 



% Zool. Jahrb., xiv. (1900) pp. 1-60 (4 pis. and 23 figs.). 



