328 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Development of Gonophores in Siphonophora.* — W. Richter lias 

 studied this in Rhizophysa, Physalia, and Hvppopodius. Only some of 

 the more general facts elucidated in the paper can be quoted here. 

 In all the gonophores — male and female — examined, the origin of the 

 radial canals from stomach-grooves, independently of the bell-nucleus, 

 is established. The germ-cells arise in the endoderm ; only in Physalia 

 could the ectodermal origin of the spermatoblasts be proved with any 

 probability. In none of the forms does a wandering of the germ-cells 

 to the ectoderm take place. The development of the gonophores into 

 the medusoid structure goes on in the usual way in the female gono- 

 phores and in the male of Hippopodius. The male of Rhizophysa shows 

 a simplification in so far as that a typical bell-cavity is not developed ; 

 further development is by a downwardly directed growth, accompanied 

 by a progressive blending of the tamiolas edges. The most important 

 result is the demonstration that the old A^assiz-AVeismann theorv of the 

 origin of the Medusa cannot be held for the Siphonophora, as Goette has 

 already shown for the Hydromedusae. A new light is here thrown upon 

 the question of the origin of the Siphonophora from the Hydromedusae. 



Australasian Hydroid in North Sea.f — James Ritchie gives an inter- 

 esting account of a colony of S&rtularia elonyata picked up in the North 

 Sea. The colony was complete, with naturally terminated stems and 

 perfect pinnae, upon practically every one of which in the more mature 

 colonies are perched exceedingly delicate, loosely attached gonangia. 

 The preservation of these delicate structures is regarded as evidence 

 that the colony was not artificially transported, e.g. in ballast on board 

 some ship loading at an Australasian port, but was borne on ocean 

 currents. 



Nuclear Cycle of Gonionemus murbachii A. G. Mayer.} — H. B. 

 Bigelow gives an account of the mitosis in the somatic cells of adult 

 tissues of this Ccelenterate, of its entire course of spermatogenesis, the 

 early nuclear development of the oocyte, and the nuclear phenomena 

 connected with fertilisation. An interesting point is that in fertilisation 

 nuclear union may take place either by fusion or by apposition ; the 

 determining factor is believed to be the relative sizes of the nuclei at 

 the time of their union. In the first cleavage spindle there are the full 

 number of somatic chromosomes. In the second cleavage there is a 

 reduced number, each of which is a bivalent structure resulting from 

 the pairing of univalent chromosomes. The number of chromosomes 

 in the third cleavage has not been observed, but in the fourth and 

 subsequent cleavages all nuclei have the full somatic number of 

 chromosomes. 



Porifera. 



Coalescence and Regeneration in Sponges.§ — H. Y. Wilson de- 

 scribes the formation of plasmodial masses in moribund specimens of 

 Mkrociona prolifera. When fragments are squeezed through a cloth so 



* Zeitschr. Wiss. Zool., lxxxvi. (1907) pp. 557-618 (3 pis. and 13 figs.). 

 t Proc. Roy. Phys. Soc. Edinburgh, xvii. (1907) pp. 80-3 (1 pi.). 

 X Bull. Mus. Comp. Zool. Harvard, xlvii. (1907) pp. 287-399 (8 pis.). 

 § Journ. Exper. Zool., v. (1907) pp. 245-58 (4 figs.). 



