670 SUMMARY OF CURRENT RESEARCHES RELATING TO 



is that both antennae in the female and the left in the male have twenty- 

 six joints, and the right in the male twenty-three. No other member of 

 the Gymnoplea is known with more than twenty-five. 



Oogenesis and Spermatogenesis in Cyclops strenuus.* — P. Lerat 

 finds that the general sequence of kinetic processes is the same in 

 oogenesis and spermatogenesis. The only noteworthy difference is in 

 the volume of the cells. In the zone of multiplication all the cells have 

 the normal number of chromosomes. The numerical reduction does not 

 precede the first maturation-division. During the period of synapsis, 

 the chromatin forms filaments which unite in pairs to form a thick 

 spireme and are afterwards separated in an apparent longitudinal divi- 

 sion. The maturation divisions are the same in the two sexes. The 

 first division is heterotypic : there is a true longitudinal cleavage of the 

 chromosomes ; the second division is homotypic ; and in the hetero- 

 typic division the numerical reduction of chromosomes is effected. 



Anuulata. 



Bionomics of Annelids.f — G. Bohn gives an account of the be- 

 haviour and general functions of Annelids. In a preliminary section 

 he deals with the organisation and functions of the organs, discussing a 

 typical segment, differentiation of segments, different regions of the 

 body, and variations in the number of segments. The next section 

 treats of the classification, which, it is pointed out, is an ethological one ; 

 the bathymetric distribution of marine Annelids ; the different habitats 

 — rock, sand, mud, etc. ; and the different modes of life, tubicolous,. 

 commensal, etc. Then follows a consideration of the different families, 

 under which, in all, seventy-three species are dealt with as regards their 

 habitats and mode of life. 



Embryology and Affinities of Sipunculidae.J — J. H. Gerould gives 

 a very full account of the development of Phascolosoma from matura- 

 tion and fertilisation on to post-larval stages. The paper includes also 

 a comparison with Sipunculus, Chgetopods, Echiurids, Molluscs, and 

 Vermidea, and also a statement of the generic characters of Sipvncnlus 

 and of Phascolosoma. It is concluded that the Sipunculids are probably 

 primitive forms. This is shown by their unpaired, unsegmented, ventral 

 nerve-cord, by the retention in the adult of the principal retractor muscles 

 of the trochophore, and of the single pair of thoracic nephridia. The 

 entire organisation of the adult is exceedingly simple and trochoph ore- 

 like. The transitory metamerism of the trochophore of P. gouldii prob- 

 ably indicates a near relationship to that type, an incipient tendency 

 towards metamerism. Sipunculids are Annelids closely allied to the 

 Chgetopods and to primitive Molluscs, but are even simpler in structure 

 than the Archiannelida. 



Larva of Echiurus.§ — W. Salensky gives an account of the struc- 

 ture of this larva, dealing with its externals, ectoderm layer, and skin 



* La Cellule, xxii. (1905) pp. 163-99 (4 pis.). 

 t Ann. Sci. Nat. (Zool.) iii. (1906) pp. 35-144. 



J Zool. Jahrb. Abt. Anat, xxiii. (1906) pp. 77-162 (8 pis. and 4 figs.). 

 § Mem. Acad. Lmper. Sci. St. Petersbourg, series 8, Classe Pbysico-Mathe- 

 rnatique, xvi. (1905) pp. 1-102 (10 pis.). 



