42 DK. W. RAE SHERRIFPS ON EVOLUTION 



with ventrally and laterally nothing more than minute cylindrical 

 corpuscles. D.fusca with indefinite double rows of about 6 pairs — 

 on a slightly higher level, but also showing primitiveness in 

 numerous quite small elements. D. savignyi with indefinite 

 steep double rows reduced to 6— somewhat higher, but also 

 showing, like the preceding, very numerous small cylindrical 

 bodies. 



2. In the hemprichi group : — 



Z>. clavata, where occur 10-12 pairs in each double row and a 

 veiy weak supporting bundle. It may be noted that in this 

 group we have a gradual reduction in the number of spicules 

 composing each point 5-7, 5-6, 4, 3, 2 and 1, reaching a climax 

 in forms like D. pimicea, where are found a couple of slightly 

 hockey-club like spicules occupying the whole area which in 

 D. davata, for instance, shows 10-12 pairs. 



3. In the studeri group : — 



Here we have, on the whole, a more differentiated group with 

 forms like D. mayi with 6-8 pairs in each point to be ranked 

 as relatively primitive compared with the highly-specialized 

 D. kollikeri. 



§ 11. So with the Divaricates, on my view the series begins 

 with forms like D. japonica with 8 pairs in each point, none 

 protruding — a very primitive arrangement — and ends with 

 D. suensoni, which has but one pair. As intermediate between 

 grade II., which I define as having numerous pairs regularly 

 arranged in each point (grade I. possessing very numerous 

 irregular pairs), and grade III., with 5-6 equal pairs, we have 

 cases like D. armata, where the lateral points go up to 9 pairs. 

 There must also be noticed D. coeridea inclining to be primitive in 

 minuteness but not in number of spicules, while D. Munzingeri 

 may be considered as rising out of grade II. because one of the 

 uppermost pairs is very prominent. 



It is interesting to see that in so many of Kiikenthal's minor 

 groups his arrangement of the species ends in one pair, so that 

 the anthocodial armature, which I hold to be the evolutionary 

 key, is, as used by Kiikenthal, very probably just diagnostic. 



Again, in the rigida group, D. microspiculata is undoubtedly 

 primitive with 6-8 pairs, though the uppermost again is slightly 

 larger and projecting. 



§ 12. In the third great division— the Umbellates — grade I. is 

 represented by D. australis with its very numerous, small polyp 

 spicules, grade II. perhaps by D. umhellulifera with 6-8 pairs and 

 the practical absence of a supporting bundle. 



In the dendrophyta group, Z>. viUosa belongs to grade I. with 

 many spicules in each double row, while grade II. in the florida 

 group may be illustrated by D. brevirama (with 6-8) and D. florida 

 (with 5-7). 



