ITS SUMMARY OF CURRENT RESEARCHES RELATING TO 



INVERTEBRATA. 

 Mollusca. 



•y. Gastropoda. 



Germinal Layers in Gastropods. * — T. Fujita has studied the- 

 formation of the germinal layers in Siphonaria lepida and in Aplysia, 

 and compares his results with those attained by others. Throughout 

 the cleavage there is no fixed regularity, such as is expressed in the so- 

 called law of alternation of spirals as stated by Wilson, Kofoid and 

 others. There is, however, a spiral arrangement or symmetry for some 

 time. It is abruptly transformed in an interesting manner into a 

 bilateral symmetry, just after the cells of three germ-layers are dis- 

 tinguishable. The author follows the lineage on to the 50-cell stage, 

 and sums up in a table of cell-generations, which he compares with 

 similar tables of Neritina, Umbrella, and Limax. 



Maturation in Nudibranchs.f — W. M. Smallwood has studied the 

 eggs of Doris bifida, Montagua gouldii and M. pelosa, at Wood's Hole,. 

 Mass. 



The chromatic substance is differentiated into basi-chromatin and 

 oxy-chromatin. The former gives rise to the chromosomes ; the latter 

 passes into the cytoplasm, to contribute in part to the formation of the 

 sphere substance. 



No evidence of chromosome vesicles was found during the prophase 

 of the first maturation, as is the case in Haminea solitaria. But during 

 the " rest-pause " between the first and second maturation, the chromo- 

 somes frequently have distinct vesicles. 



The Qgg chromosomes enclosed in vesicles change while in this state, 

 until each vesicle has the appearance of a miniature nucleus. Before the 

 metaphase of the second maturation, the several chromatic granules unite 

 into a solid mass, the vesicle probably disappearing. The facts observed 

 strengthen the growing conviction that the theory of the qualitative 

 division of the chromosomes is untenable. 



Fertilisation takes place in the oviduct, the tail remaining outside. 

 The sperm head becomes vesicular during its progress towards the animal 

 pole ; and while it is undergoing this change one or more chromosome 

 vesicles may be formed, in connection with the chromatin derived from 

 the sperm, which are similar to the egg chromosome vesicles. These 

 vesicles arise undoubtedly through the influence of the chromatin on the 

 cytoplasm, and this fact suggests Lhat the vesicles in the three Nudibranchs 

 investigated are not identical with those in Haminea solitaria, which arise 

 in the nucleus. 



Magellan Species of Trophon4 — H. Strebel reports on the species of 

 Trophon from the Magellan province collected by the Swedish Expedi- 

 tion (Nordenskjold), the Scotia Expedition (Bruce), by Michaelsen, bv 



* Journ. Coll. Sci. Univ. Tokyo, xx. Article 1 (1904) pp. 1-42 (3 pis.). 

 t Morphol. Jalirb.. xxxiii. (1905) pp. 87-105 (1 pi.). 

 X Zool. Jahrb., xxi. (1904) pp. 171-248 (6 pis.). 



