ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 443 



He gives a diagnosis of the family and a key to the genera (Archicon- 

 chmcia Muller, Gonchoecia Dana, and Halocypris Dana. Ten species are 

 described, G. ritteri being new. 



Annulata. 



Sexual Reproduction in Jllosoma.* — Jas. A. Nelson describes the 

 rare occurrence of sexual reproduction in this primitive Oligochget. In a 

 number of specimens ten were found with sex-elements ; four contained 

 ova only, three contained male elements only, three contained both. 

 The spermatogenesis is discussed, and one point is especially noteworthy 

 —the appearance of a large nucleolus in the spermatocytes of both orders 

 and in the spermatids. This indicates the very unusual occurrence of a 

 long resting stage between the two maturation-divisions, and also a long 

 pause before the metamorphosis of the spermatid into the spermatozoon. 

 It is not known what conditions determine the occurrence of sexual 

 reproduction. 



Ethology of Tubifex and Lumbriculus.f — F. von Wagner com- 

 municates some ethological notes on these Oligochasts. Thus Tubifex, 

 much more than Lumbriculus, is an inhabitant of mud. Autotomy is 

 much less important in Tubifex than in other related forms ; its wide- 

 spread abundance makes this capacity less necessary. The astonishing 

 energy of Tubifex, which may continue in active movement for four 

 hours without interruption, is commented on. The author discusses the 

 highly developed autotomy of Lumbriculus, the tube-making of Tubifex, 

 and the frequent association of the two forms. The excellent illustra- 

 tions of Tubifex in its natural surroundings deserve special notice. 



West Indian Polychsets.j — H. Augener reports on a collection of 

 about eighty Polychajts collected by the ' Blake.' About a third of the 

 species were previously described by Ehlers in his " Florida Annelids " 

 (1887). The majority of the species are West 'Indian and mid-Atlantic 

 forms ; four are known from the Mediterranean ; about a dozen are 

 known from mid- Europe and North Europe, and also for the most part 

 from North American coasts ; five are known also from the West African 

 region. Twenty-one families are represented. 



Artificial Parthenogenesis in Thalassema.§ — George Lefevre finds 

 that the ova of Thalassemia mellita Coun, exposed for a short time to 

 dilute solutions of acids, may undergo normal development, although 

 the rhythm of division is more or less disturbed, and may give rise to 

 normal larvae. The reduced number of chromosomes, after normal 

 maturation-mitoses, persists, and was repeatedly verified in late blastula- 

 and gastrula-stages. 



In some cases, however, only one polar body was extruded ; in some 

 cases neither was formed. Upon sectioning these eggs, it was found that 

 either one or both maturation-mitoses had taken place well below the 

 surface, without accompanying cytoplasmic division. Many abnormal 



' Ohio Nat., vi. (1906) pp. 435-8 (5 figs.). 



t Zool. Jahrb., xxiii. (1906) pp. 295-318 (1 pi.). 



% Bull. Mus. Comp. Zool. Harvard, xliii. (1906) pp. 91-196 (8 pis.). 



§ Science, xxiii. (1906) pp. 522-4. 



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