NOTES ET REVUE xix 



females in the vicinity antl liastens tlie tle|)osil of e^^s, wliich ;in' 

 forcibly ejected in showers. 



A few hours before egg-laying occurs, llie ncphiidia I..-.(iiih' 

 distendedwith a clear Huid, which is perhaps sea watcr, inlo wliicli 

 the sexual products are swept. General muscular relaxation, which 

 is caused in part by weak illuuiination, facilitâtes this |)n)(;css. 

 The time of egg-laying (usually helween 8 p. ni. ami ia. m. can 

 be hastened only very slightly by keeping tlie anini.ils in Ihr ilark. 

 There is an established rhythm in egg-laying, which is indcpciKh-iil 

 at présent of external surroundings. 



Maturation and Fertilization. The buUet-shaped hcad of Ihc 

 spermatozoon,uponentrance into the cytoplasm, rotâtes ISO^ahmil 

 its transverse axis, and a small astrosphere, wtiich contains a 



«ne 



Fie. \. 



Fig. 2 



FiG. 1.— Chromosomes of the (irst maturation si)iii(lle,vlevveil fnmi Ihc sidi'. 



Fig. 2.— Cliromosomes of the second maturation spindie, as seen in a secticm iil.lii|ne 

 to the long axis of the spindle. 



minute centrosome, appears at its ba.se in the région of Ihc iniddlc 

 pièce. At this time, the protoplasmic processes whicii surroiind Ihc 

 egg disappear, and are probably retracted into the cytoplasm. The 

 astrosphere précèdes tlie sperm nucleus to the centre of tiie egg, 

 whilethe first polar body is being fornied. A deeply-staining rod 

 connects the astrosphere with the nucleus. liaving reached the 

 centre of the egg, both sperm nucleus and its centrosome incn-.ise 

 greatly in size, but neither of them divides. 



The spindle of the first maturation division has ten chromosomes 

 (the reduced numberi, which hâve the shape of elongaled rings or 

 rods, which lie parallel to its long axis (Kig. 1). Thèse rings break 

 apart in the middle by a réduction division, each forming lw<. 

 U-shaped chromosomes, which are characteristic of the second 



