W. G. VanName — Embryology of Eustylochns. 267 



94) he says of this species : " 1 have referred this with considerable 

 doubt to Girard's species, for the description of the latter was very 



meagre The generic relations of this species are somewhat 



doubtful In many respects the reproductive organs are like 



those of Eustylochiis, and it is possible that the affinities may be 

 even greater with that genus than with PlanoceraP 



This question I have not had the material or the opportunity to 

 investigate. The species is, however, a strongly chai-acterized one, 

 both in appearance and habits, and is readily recognizable, so that 

 no confusion will be caused should it prove necessary to transfer it 

 to another genus. It is an exceedingly active creature and crawls 

 with considerable rapidity, for a planarian, while Eustylochus ellip- 

 ticus is very sluggish and moves but little unless disturbed. 



The eggs are larger than those of Eustylochus ellipticus, measur- 

 ing 0*090™™ or more, but the amount of shrinkage which occurs in 

 preserving the eggs and in imbedding them is so variable that in 

 sections they often appear no larger than those of Eustylochus. 

 The}' are surrounded by a membrane considerably larger than the 

 ^gg, but in this species it is much thinner, the amount of mucus 

 present about them is less, and they are not laid so close togethei-. 



The difference in the size of the eggs of the two species does not 

 seem to affect the size of the mitotic figures, pronuclei or polar 

 bodies, but results simply from an increased amount of cytoplasm 

 and yolk. 



The descriptions and figures in the remainder of this paper are 

 taken from eggs of Eustylochus unless otherwise stated. Neverthe- 

 less the resemblance between the eggs and embryos is so close that 

 they would apply almost equally well to Planocera nebulosa. Dif- 

 ferences of any importance between the two species have been noted. 

 The methods of preparation used were the same in the case of both 

 species. 



Methods of Preparation. 



As I have already intimated, it was necessary to depend entirely 

 upon sections for studying the internal processes of development* 

 In preserving the eggs a number of different reagents were tried ; 

 saturated solution of corrosive sublimate both with and without the 

 addition of two per cent, of glacial acetic acid or one and one-half 

 per cent, of nitric acid, picro-acetic containing one per cent, of 

 acetic acid, seventy per cent, alcohol with five per cent, of glacial 

 acetic acid, Gilson's, Hermann's, Flemming's and Perenyi's fluids. 



