THE STAEFISH SOLASTEE EXDECA. 9 



My own observations on S. papposa, made from serial sections of an interradius in 

 a half-grown specimen, showed only two external apertures (one for each gonad). 

 Each of these led to a crypt-like cavity, into the bottom of which several egg-ducts 

 opened. Eversion of this cavity may occur during later growth or at the periods 

 of ripeness, thus producing the condition described by the authors above named. 

 For a further discussion of these points, see under reference 8 a. 



III. Matukation, Spawning, Feetilization, &c. 



Maturation. — Preparation for the maturation-changes begins after the egg has 

 reached full size, and while it is still attached to the gonad-wall. The germinal vesicle 

 elongates radially and migrates towards the attached side of the egg until one of its 

 poles lies close under the surface. The nucleolus becomes vacuolated, ceases to react 

 actively to stains, and finally disappears. Meantime the membrane of the germinal 

 vesicle has broken down. The contents remaining in position help to form a tract or 

 plug, which is free from fatty yolk-granules and extends right to the centre of the egg. 

 This tract comes to the surface in the middle of what will afterwards be recognizable 

 as the upper pole of the egg. Here it expands into a small circular disc. After the 

 eggs are shed this disc appears under reflected light as an area slightly darker than 

 the rest of the surface, no doubt owing to its greater transparency and freedom 

 from yolk. 



In the ova examined, the formation of the first polar body was in active progress at 

 the time of shedding. An egg fixed immediately after extrusion showed the first 

 of the spindles lying obliquely within the disc above mentioned and close under the 

 surface. In eggs fixed three hours after extrusion both polar bodies were found 

 extruded and adherent to the surface, while the small female pro-nucleus, now difficult 

 to detect, lay some distance below. No doubt the pro-nucleus next migrates towards 

 the centre of the egg. 



Spawning. — Apparently the brooding-habit is absent. Spawning occurs in the end of 

 March or the beginning of April, and extends at intervals over a week or more. For 

 example, a specimen taken in the trawl off the Marine Station at Millport on 

 March 22nd, 1910, gave out ova on the 25th, on the 30th of the same month, and 

 again on April 2nd. No further spawning took place, although the specimen was 

 kept under observation for the next four weeks. The number of eggs on the first 

 occasion is not known approximately, but on the second it amounted to over three 

 thousand, and on the third to between two and three hundred. On the second 

 occasion (March 30th) the period of most active spawning lasted about two hours. 

 During this time the Starfish was attached to one side of the tank near the surface, 

 the body and arms being strongly arched so that only the tips of the latter were 

 adherent. The ova could be seen emerging as many as four at a time from the genital 



VOL. XX. — PART I. No. 2. — February, 1912. c 



