E. MARSHALLI. — YOUNG SPECIMENS. 115 



systems are actively increasing the nnmber of their beams. As 

 such may be regarded Nos. 1-17, given in the table (say, speci- 

 mens ranging from 20 to 90 mm. in length). From the data 

 afforded, I think it safe to give the range of numerical increase, 

 in these S23ecimens, of the transverse beams as from 32 to 52 or 

 even up to great deal more (say, an increase of 20 and over), 

 and of the longitudinal beams as from 25 to 38 (an increase of 

 13, which is likely about the maximum limit). It can not then 

 be gainsaid that, during the life-period represented by these 

 specimens, the former increase in number with greater rapidity 

 than the latter, — a fact which, so far as it goes, conforms to the 

 general tenor of Schulze's statement. 



Should however a young specimen of E. marshalli be brought 

 into direct comparison with an old one as regards the points in 

 question, one may be misled into quite different inferences. For 

 instance, by comparing specimen No. 2 (of the table) with No. 

 28, the appearance is that the rates of increase of the two kinds 

 of beams have kept pace together, both showing alike an increase 

 of 12. It may even be found, as e.g. by comparing Nos. 2 and 

 30, that the longitudinal beams have increased far more than the 

 transverse. It is plain that these appearances are due to the 

 fact that the longitudinal beams have continued to multiply 

 themselves after the transverse have ceased to do so. 



I think what has been said above concerning the increase 

 of the skeletal beams is, in the main, applicable to all species, 

 or at least to those in which the synapticular fusion of spicules 

 never takes place. In E. imperlalis, which is one of the species 

 with a partially rigid skeletal framework, the multiplication of 

 the beams is made impossible as soon as the amalgamation of 

 their elements sets in and so far as this extends in the lower 



