522 E. A. MINOHIN. 



each such granule corresponds to a spine. In the smooth 

 spicules, on the other hand, the granules seem to be about to 

 form a second nucleus, and. this is perhaps the manner in 

 which nuclear division takes place ; but I have not succeeded 

 in finding an actinoblast containing two definite nuclei, but 

 only the state of things shown in fig. 30, one nucleus and a 

 bunch of granules. If this really represents nuclear division 

 it would be rather an unusual type, though essentially similar 

 to the manner in which, according to Fiedler (1888), the 

 nucleus of the ovum of Spongilla buds off" little masses of 

 chromatin which represent the polar bodies. 



In reticulum (PI. 40, figs. 33 — 37) some quadriradiates 

 have the fourth ray comparatively short (fig. 35), while others 

 have it excessively long (fig. 37). The former have one 

 nucleus, the latter two, in the actinoblast. It is very easy to 

 find instances in which the nucleus has only recently divided 

 (figs. 33, 34, and 36), though I have not seen the actual process 

 of nuclear division, but this would probably be a favorable 

 object in which to study it. The interesting point to notice, 

 from the point of view of the growth of the spicule, is the 

 variation in the period at which nuclear division takes place. 

 We may assume that if the two nuclei are close together the 

 division must have taken place recently, since they afterwards 

 become so widely separated, as shown in fig. 37. In this way 

 we see that the division sometimes takes place at an extremely 

 early period (figs. 33 and 34), and sometimes only after the 

 ray has attained a considerable size, as in fig. 36, where the 

 small size of the two nuclei is a further proof of their recent 

 division. Thus it would seem as if a ray was sometimes 

 destined from the first to attain a great length, while at other 

 times an elongated ray arises by some change at a later period 

 in the secreting cell of a ray originally destined to be short. 

 From the large number of spicules that occur with gastral 

 rays similar to that drawn in fig. 35, it can hardly be doubted 

 that many never go beyond this stage, and are, so to speak, 

 adult spicules. But a comparison of figs. 35, 36, and 37 shows 

 how gastral rays of the short kind may be converted into rays of 



