ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 439 



regeneration of the head-ganglia in Protodrilus flavocapitatus Uly. The 

 process is very rapid and the restoration is complete, except that the 

 eyes were only regenerated in 3 out of "200 cases. In the restoration of 

 the anterior end of the gut, there is a co-operation of ectodermal and 

 endodermal cell-groups. The head-ganglia appear as a group of spheri- 

 cal cells on the ventral side below the mouth, and are gradually shunted 

 upwards, separating off from the epidermis, and differentiating Punkt- 

 substanz on the posterior inner side. In the regeneration of the tail 

 end the tip is first formed, and new segments are interpolated from 

 behind forwards between the tip and the old segments. 



Artificial Parthenogenesis in Thalassema mellita.* — George 

 Lefevre finds that the eggs of this worm can be induced to develop 

 without fertilisation by immersion for a few minutes in very dilute 

 solutions of nitric, hydrochloric, sulphuric, carbonic, acetic, and oxalic 

 acids. In favourable experiments 50-60 p.c. of the eggs developed 

 into active trochophores which were strikingly normal in appearance and 

 structure. 



An egg-membrane invariably forms shortly after removal from the 

 acid solutions, and maturation, identical with the normal process, 

 frequently occurs. In a number of cases polar bodies were not extruded, 

 but sections showed that the maturation process had taken place 

 internally. In some cases four nuclei are formed in the cytoplasm, 

 which represent the egg-nucleus and the nuclei of three polar bodies. 

 These four nuclei fuse to form a cleavage-nucleus. 



The egg-centrosome disappears after the formation of the second 

 polar body, and the cleavage centrosomes are formed de novo. It was 

 frequently observed that the polar bodies continue to divide and form a 

 morula-like cluster of minute cells. Cell-divisions take place mitotically, 

 and in many cases the early cleavage is perfectly normal, although a 

 great variety of abnormal cleavages also occur. 



Sexual Forms in Fresh-water Nereids.j — Ch. Gravier discusses a 

 new fresh- water Nereid (Perinereis Kinberg char, emend.) found by 

 G. Seurat in a rain-water basin in one of the low islands (Tarauru-roa) 

 of the archipelago of Gambier. Some specimens of this Periaereis 

 seurati sp. n., have ova in various stages of development, and the body- 

 wall is reduced to a delicate semi-transparent sac with little musculature. 

 There is a very slight trace of parapodial modification, namely, very 

 vascular foliaceous lobes, a mere hint of the epigamous transformation 

 of marine relatives. 



Crystals in Hirudo and Pontobdella.J— W. Kolmer found in 

 preparations of ganglion cells of these leeches which had been fixed in 

 5 p.c. formalin, numerous crystals of a clear ruby colour, strongly re- 

 fractive and in most cases apparently belonging to the rhombic system. 

 No hint of them was found in any other tissue, and it is not known 

 whether they are present during life. 



* Science, xxi. (1905) p. 379. t Comptes Rendus. cxl. (1905) pp. 15G1-2. 



X Anut. Anzeig., xxv (1904) pp. 018-21. 



