OBSERVATIONS ON THE GEEGARINES OP HOLOTHURIANS. 289 



difficult to be certain of. Their typical arrangement appears 

 to be in two rows of four^ with the nucleus towards the narrow 

 or infundibular end of the spore, and the tail pointing away 

 from it. Nevertheless variations occur constantly from this 

 position, one or more of the sporozoites being turned round 

 with the tail towards the spore-funnel. The thin diaphragm 

 at the base of the funnel is probably the spot at which the 

 spore- wall breaks to liberate the sporozoites, and the more or 

 less constant position of the latter, with their heads turned 

 towards the funnel, doubtless is in connection with this fact. 

 It is probable that the sporozoites are motile within the spore, 

 which would account for their not unfrequent reversal of 

 position. 



They very often appear closely applied to the wall of the 

 spore. Since the tails of the front row overlap the heads of 

 the hinder row, we can understand how it is that all the eight 

 are to be seen in section. They lie embedded in the granular 

 mass or ^^ nucleus de reliquat^' (sporophore — Wolters) filling 

 the spore, which doubtless serves as nourishment for the 

 growing sporozoites. If we compare fig. 15, b, or 16, a, with 

 fig. 13, c — g, which are drawn to the same scale, it is evident 

 that the bulk of the nucleus of a sporozoite is about half that 

 of a nucleus of a spore in the last stage, and it is scarcely to 

 be doubted that each nucleus in the stage with four nuclei has 

 divided in two to furnish two sporozoite nuclei, which elon- 

 gate to form the '' head " of the sporozoite, while protoplasm 

 becomes aggregated round them to form the tail. In the four 

 cysts which I cut into sections I was able to find two stages 

 of the sporozoite. The first is shown in fig. 16 : a represents 

 a spore in which six sporozoites could be seen ; b and c show 

 two other spores, one showing five sporozoites, the other in 

 transverse section showing eight, both magnified about 1000; 

 d, e, and /show three sporozoites much more magnified. In 

 this stage the nucleus is not more than twice as long as broad, 

 and the tail is short and stumpy. The second stage, and 

 probably the final one, is shown in figs. 15 and 17, and in fig. 

 18, which is a combined semi-diagrammatic figure. The nucleus 



