464 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Nais with bifurcated Prostomium.* — Prof. C. M. Child describes 

 a case of Nais lacustris in which the proboscis-like prostomium is bifur- 

 cated, probably as the result of an injury. One point is of special 

 interest ; — the branch is about as long as the main prostomium ; i.e. a 

 new prostomium of full length has arisen from a point near the tip of the 

 original prostomium, just as it would arise if the latter were cut off at 

 its base. If this be the result of regenerative processes, the lateral 

 region of the prostomium, as well as its base, is capable under certain 

 conditions of giving rise to a prostomium of full length. 



Reproductive System of Digaster.f — Sarah 0. Brennan describes 

 the reproductive organs of the earthworm, Digaster (Didymogaster) 

 8ylvaticus, supplementing the account given by J. J. Fletcher in his 

 diagnosis of the genus in 1886. She describes a pair of ovaries, two 

 oviducts, three pairs of spermathecae, two pairs of testes, two pairs of 

 funnels leading into a pair of vasa deferentia, two pairs of lateral seminal 

 vesicles, two median sperm reservoirs, occupying a segment each, and a 

 pair of bilobed spermiducal (prostate) glands. 



Oligochaeta from Illinois.^ — Mr. Frank Smith gives a list of the 

 Oligoebaetes found near the Biological Station at Havana, Illinois, 

 with descriptions of the Tubificidae. Among the latter the most interest- 

 ing form is a new one described as Rhizodrilus lacteus g. et sp. n., 

 which occurs in the " bottom-lands " of the Illinois River. It is distin- 

 guished from all known Tubificidae by the " presence of two distinct 

 kinds of highly modified genital setae, and the presence of such setae in 

 the ninth somite." It is possibly related to Vermiculus, and in regard 

 to its circulatory system is perhaps the extreme form of the series con- 

 stituted by Vermiculus sp. and Ilyodrilus coccineus. Another interesting 

 form described in some detail is Embolocephalus multisetosus sp. n. 



Development of Nephridia.§ — F. Vejdovsky discusses the points at 

 variance between himself and Bergh as to this question. In part the 

 differences in statement of the two authors would appear to be a dif- 

 ference in terminology. According to Vejdovsky the contractile bladder 

 (Endblase) is of ectodermic origin, while Bergh says that the ter- 

 minal region {Endabschnitt) is of mesoblastic origin ; but according to 

 Vejdovsky the exact significance of the last term is not adequately 

 defined. Vejdovsky figures and redescribes his sections in order to make 

 his own position perfectly clear. The sections show, as he believes, 

 without a possibility of error, that in Lumbricidse, as in Tubifex and in 

 Rhynchelmis, the terminal bladder arises as an ectodermic invagination 

 without any primitive connection with the nephridium primordium. 



Metamerism of Hirudinea.il — Mr. W. E. Castle has re-investigated 

 this subject. He finds that the number of somites in the body of the 

 leech has been determined correctly by Whitman (1892) for the Rhyn- 

 chobdellidae, and by Bristol (1899) for the Gnathobdellidas. In both 

 cases the number is thirty-four. The limits of the leech somite have 



* Anat. Anzeig, xvii. (1900) pp. 311-2 (1 fig.). 



+ Proc. Linn. Soc. N. S. Wales, xxiv. (1900) pp. 691-6 (2 pis.). 



% Bull. Illinois State Lab., v. (1900) pp. 441-58 (2 pis.). 



§ Zeitschr. wiss. Zool., lxvii. (1900) pp. 247-54 (1 pi.). 



"|| Proc. Amer. Acad. Sci., xxxv. (1900) pp. 285-303 (8 figs.). 



