326 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



rived from rods, and these rods or chromosomes do not undergo reduc- 

 tion either before or during the formation of the polar bodies, but 

 only at the beginning of the first figure of segmentation. 



In Glepsine similar results were obtained in regard to the polar 

 corpuscles, polar spheres, &c, but there are certain complexities in regard 

 to the history of the nucleolus. An interesting point is that when the 

 eggs are detached, and are lying freely in the ovarian cavity, they are 

 still surrounded by their follicular membrane. 



American Oligochgeta.* — Dr. Gustav Eisen publishes a monograph 

 on this subject, based on collections made in North America, especially 

 on the Pacific coast and the adjacent islands. In Mexico and Central 

 America a form provisionally regarded as merely a sub-species of 

 Pontoscolex corethrurus is very abundant, and its minute characters are 

 described in some detail. Among the points regarded by the author as 

 of special j>rotective value, and therefore as helping to explain the wide 

 distribution of the members of the genus, are the following : — (1) In the 

 anterior segments the muscle-layers are separated by spaces, which the 

 author believes enable the body to expand suddenly, and so cling to 

 the burrow ; (2) the caudal zone (" zone of growth " of Schmarda) is espe- 

 cially sensitive, and can also suddenly expand, thus enabling the worm 

 to perceive and resist a sudden attack ; (3) the posterior end of the 

 body has a corkscrew twist which must also enable the worm to cling 

 closely to the soil ; (4) the epidermis contains complex " auditory " 

 cells. 



The genus Ocnerodrilus is split up into a number of sub-genera, of 

 which one, Nematogenia, is characterised by the presence of peculiar 

 spirally coiled lymphocytes (nematocytes), not hitherto described in 

 Oligochaetes. 



An interesting new species of Benhamia is described, which is bright 

 green in colour, and in the position of its spermiducal pores connects 

 the genus with Dichog aster. It is indeed now possible to draw up a 

 perfect series from tbe Benhamia condition on the one hand to the Dicho- 

 gaster condition on the other. 



In an appendix is a brief but interesting note on the disappearance 

 of native forms before the hardier European species. In California 

 and the Southern States it is now impossible to find in rich garden soil 

 or manure heaps anything but imported species. Among the causes of 

 this replacement the author notices the following : — the native forms are 

 pale-coloured and are more sensitive to heat and light than the hardy 

 deeply-pigmented European species. Again, the imported forms thrive 

 best in cultivated soil, while cultivation drives the native species away. 

 The latter have a short breeding season, and must therefore reproduce 

 less rapidly than the European forms with their longer period of matu- 

 rity. The replacement takes place, however, in the case of Terricolse 

 only, few of the European Limicoline forms having as yet obtained a 

 foothold. 



Oligochseta of Illinois.!, — Mr. F. Smith gives a list of species from 

 this region, and descriptions of two Tubificidae — Bhizodrihs lacteus g. 



* Proc. California Acad. Sci., ii. (1900) pp. 85-276 (10 pis.), 

 t Bull. Illinois Lab. Nat. Hist., v. (1900) pp. 441-5S (2 pis.). 



