ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 583 



horizontal cut affects the cleavage but little. If the blastomeres are 

 separated by a vertical cut near the end of the first cleavage, partial 

 cleavage takes place as in the blastomeres isolated at the 2-cell stage. 



If a portion of cytoplasm is cut off from the vegetal region at the 

 2-cell stage, the size-relation of the upper and lower cells of the 8-cell 

 stage is normal, irrespective of the angle of the section. In the e^ 

 compressed between two planes parallel to the main axis of the egg, the 

 second cleavage is equatorial ; and upon relieving the pressure, the third 

 cleavage is vertical and perpendicular to the first. 



The following results were obtained from the study of the egg of 

 both Cerebratulm Jarteus and G. marginatus : — 



In the eggs kept in sea-water without calcium-salts, the third cleavage 

 is vertical, resulting in eight blastomeres arranged either in a ring or in two 

 parallel rows. In the trefoil egg the second cleavage is vertical, giving 

 rise to six blastomeres arranged in a ring. Irrespective of the number 

 of the initial blastomeres (basal cells) formed by vertical cleavages, the 

 division goes on normally in each of them. 



Nematohelminthes. 



New Nematode from Trinidad.*— R. T. Leiper describes Lago- 

 chilascaris minor sp. n., which causes subcutaneous abscesses in natives in 

 Trinidad. The peculiar shape of the three lips, and the presence of a 

 narrow keel-like ridge of cuticle on either side of the body throughout 

 its length, distinguish this form from the three species of AscaridaB 

 knownto occur in man, viz. Ascaris lumbricoides, Belascaris mystax, and 

 Toxascaris marginata. The alimentary canal is the normal habitat, and 

 its occurrence in abscesses under the skin renders it likely that some 

 other host — probably one of the Carnivora — and not man, is its normal 

 host. 



Botifera. 



Life-cycle of Hydatina senta.f — A. F. Shull has made an ex- 

 perimental study of the causes that determine the transition from the 

 parthenogenetic to the sexual mode of reproduction in the Rotifer Hyda- 

 tina senta, and has obtained results which seem to him to go far towards 

 bringing previous contradictory conclusions under a single point of view. 

 He has been able to secure winter eggs and males from the same parent, 

 and finds that, as has long been suspected, male eggs and sexual eggs 

 are identical. His experiments show that the presence of other sub- 

 stances than food in the water exert a strong influence on the 

 inauguration of the sexual phase. To test this influence, the experi- 

 menter used water from old cultures, from which the Protozoa had been 

 removed by filtering. This filtrate was used in various strengths, and 

 cultures were also made in pure spring water. The results of the 

 various experiments are tabulated, and in every case the evidence points 

 to the same conclusion : that the filtrate from the old cultures reduces 

 the number of sexual females. A further set of experiments was under- 

 taken to test the apparent effect of starvation. Each time there was a 



* Proc. Zool. Soc, 1909, pt. iv. (published 1910) pp. 742-3. 

 t Amer. Nat., xliv. (1910) pp. 146-50. 



