614 SUMMARY OF CURRENT RESEARCHES RELATING TO 



poration of segments arising in this pre-abdominal region. The mefca- 

 meres retain a certain plasticity and autonomy which admits of their 

 being modified and adapted to new physiological or mechanical conditions 

 in the course of development. 



Nematoh.erminth.es. 



Life-Span of Filaria medinensis.* — Sir Patrick Manson notes that 

 opportunities for ascertaining with approximate accuracy the duration 

 of the life-span of the guinea-worm are rare, and he therefore gives 

 two cases which substantiate the general view that about a year must 

 elapse between the infection from Cyclops and the emergence of the 

 worm on the surface of the skin. The season of infection is correlated 

 with the annual recurrence of certain conditions of moisture and tem- 

 perature favourable to the Cyclops and to the development of its 

 parasite. 



Unfertilised Ova of Ascaris in Human Fseces.t — K. Miura and 

 V. Nishiucki describe the appearance of unfertilised ova of Ascaris 

 lumbricoides in human faeces. When they occurred alone, apart from 

 fertilised ova, only females were obtained from the patient. In the 

 uterus of these females there were no spermatozoa, and the nuclei of the 

 ova were in a resting stage. Attempts to hatch the unfertilised ova 

 were futile ; there was no segmentation. The appearance of the un- 

 fertilised ova is quite different from that of the familiar fertilised ova. 



Platyhelminth.es . 



Life-History and Reproduction of Planaria maculata.J — Winterton 

 C. Curtis finds that apparently similar specimens of this Planariar. 

 collected from different localities show considerable differences in their 

 life-histories. Some seem to have reproduced exclusively by fission, 

 others only by the sexual mode, others by both at different seasons. It 

 may be that the asexual mode replaces the sexual mode for a term of 

 years. 



The normal fission in Planaria maculata occurs without the previous 

 appearance of any furrow at the place of division and without any 

 previous development of the new organs necessary for two complete new 

 individuals. It is as if a specimen were cut in two at a definite point 

 behind the pharynx. 



In the regeneration after normal fission there is no evidence that the 

 new parts develop by the transformation of highly organised cells to a 

 simpler type which produces the new organs. It seems rather as if the 

 parenchyma included certain cells, distinguishable from the parenchyma 

 proper, which are responsible for the new parts in regeneration and also 

 for the sex-cells of the gonads. 



The mature gonads are described for the first time, and their develop- 

 ment is also traced. A note on the development of the animal makes 



* Brit. Med. Journ., No. 2218, July 4, 1903, p. 10. 



t Centralbl. Bakt. Parasitenkumle, l t0 Abt., xxxii. (1002) pp. 637-41 (2 figs.). 



X Proc. Boston Soc. Nat. Hist., xxx. (1902) pp. 515-59 (11 pis.). 



