ON THE ANATOMY. OF HISTIUOJiDELLA HOMARI. 345 



yolk-granules behind them aiTang-ed in positions that had 

 previously been held by the arclioplasm. There is a short 

 period during which the spindle almost remains alone, the 

 astei's having completely disappeared from either end. It is 

 at this time trhat the spindle can be seen to roll over as it is 

 pushed farther and farther away from the point of rupture 

 in the body-wall by the escape fi-om the egg of fresh cyto- 

 plasm. 



In a number of experiments I subsequently ascertained 

 that this rupture of the egg and extrusion of the spindle will 

 not occur if the egg is far back in the body-cavity. The 

 body-wall ruptures at its thinnest part, which is well forward 

 in the generative region. If the egg has to move forward 

 some considerable distance under pressure, before it can 

 begin to flow thi'ough the rupture the amphiaster is usually 

 broken and destroyed. It takes place most satisfactorily 

 when the egg is only a short distance from the point of 

 rupture of the body-wall. It can only be observed to occur 

 when the amphiaster itself is fully mature. When not fully 

 formed it dissolves immediately any movement of the yolk- 

 granules takes place. Unless, moreover, the rupture in the 

 body-wall is fairly large, the amphiaster is usuallj' broken 

 in the act of being forced through, being destroyed by the 

 granules pushing it through from behind. 



In one instance the central spindle had the appearance of 

 being composed of a mass of distinct threads, some of which 

 on one side of the spindle had been injured and broken, 

 the yolk-granules appearing as small grains entangled in 

 these fibres. 



I think this obseiwatiou clearly demonstrates the truth of 

 a suggestion that has been put forward, that the achromatic 

 threads and amphiasters are firm structures, or at least more 

 I'igid than the reticulum of the cytoplasm. Gardiner (10), 

 in his paper on the egg of Polychoerus caudatus, states 

 (p. 89), "That the amphiaster is much more rigid than the 

 surrounding cytoplasm is shown by two instructive prepara- 

 tions which were the result of accident. Ova containing 



