724 SUMMARY OF CURRENT RESEARCHES RELATING TO 



and muscle. This fragment regenerates the entire alimentary canal — 

 mouth, stomach-intestine, mid-gut, and anus ; it does not regenerate the 

 cerebral ganglia or the cerebral organs or the proboscis. 



It follows that the germinal origin of the parts regenerated is not 

 very important ; that the cerebral ganglia are not required in the re- 

 generation even of very important organs ; and that the regeneration 

 occurs only on the aboral surfaces. 



The author finds no satisfaction in the theory of regeneration set 

 forth by Weismann, nor in Child's. He also points out that the phe- 

 nomena called " typical regeneration," " rnorphollaxis," ,; dedifferentia- 

 tion," and " diphagocytosis," pass into one another in these Nernerteans. 



Egg of Cerebratulus.* — N. Yatsu has made an experimental study 

 of the problems of germinal localization in the egg of Cerebratulus 

 lacteus. He finds that germinal localization does not progress for at 

 least five hours after release if the eggs are kept unfertilized. The 

 germinal localization becomes more definite on the entrance of the sper- 

 matozoon. If a portion of one of the blastomeres is cut off during or 

 after the completion of the first cleavage, no matter what plane the sec- 

 tion may strike, the resulting deformity is very slight. If horizontal 

 cuts in the animal region, or oblique sections in any region, be made on 

 both the blastomeres during or after the completion of the first cleavage 

 the effect is not great. If horizontal cuts be made along the equator or 

 above it, anenteria often result. The extension of the endoderm basis 

 is almost the same up to the 2-cell stage, that of the 4-cell stage has not 

 been determined. All h, f and ^-embryos are alike and almost normal, 

 assuming the shape of young pilidia ; ^-embryos are abnormal, the 

 shifting of the apical organ to one side being found in some cases. In 

 some of the J-embryos the apical organ fails to develop. Bilaterality of 

 egg-substances cannot be detected at the 4-cell stage. A f-embryo may 

 be perfect. At the 8-cell stage, if the horizontal cleavage is made so as 

 to cut along the equator, the upper quartet always produces an anente- 

 rion, while the lower one develops into a larva, thick-walled and devoid 

 of the apical organ. If, however, the third cleavage plane is below the 

 equator the result may be variable. The group of two animal cells and 

 one vegetal cell of the S-cell stage may develop into a perfect pilidium. 

 If blastulas and young gastrulas be bisected horizontally, the pilidium 

 from both the upper and lower halves may acquire the apical organ. If 

 the apical organ be cut off after the late gastrula or young pilidium 

 stage, it may be found regenerated in the late pilidium stage. If the 

 cleavage pattern be modified by pressure or by lime-free sea-water (ring 

 and plate-embryos) the resulting larvse have always some abnormal 

 features, yet in a general way they take the form of pilidia. In lime- 

 free water differentiation and embryogeny are inhibited ; nevertheless 

 the blastomeres increase in number. When such cell-masses are put into 

 ordinary sea- water they recover their differentiating power. On isolated 

 cells produced by lime-free water a very few cilia may be scattered 

 irregularly on the surface, while in the normal position these cells 

 acquire cilia only in a restricted area. The author considers that 

 these results suggest that there is a factor which in some way brings 



* Jourc Coll. Sci. Univ. Tokyo, xxvii. (1910) pp. 1-36 (26 figs.). 



