217 
early in the life of the individual, and apparently later no change 
in this respect takes place” (p. 91). Among the numerous types 
carefully studied in this regard Strongylocentrotus drøbachiensis 
stands foremost with no less than 33,000 specimens in all sizes 
examined; the report on this study enforces deep admiration, and 
with full right Jackson states that it opens up a line of inquiry 
which would be worth following further in these and other Echini. 
The demonstration of the different localities having their own cha- 
racteristic variations — e.g. the more primitive forms being bound 
to localities which receive a considerable increment of fresh water, 
while the more advanced forms are peculiar to the localities with 
Oceanic conditions — is the beginning discovery of the conditions 
which cause variations to occur in these forms. 
The results obtained as to the order in which the different 
Ocular plates become insert are very remarkable. In 98,55 "[o of 
"Centrechinoidea” the order was found to be I, V, or V, I; IV, II, 
III, viz. the bivial plates always being the first to be inserted, the 
unpaired ocular (III) of the trivium the last -—— a very striking 
argument in favour of Lovén's orientation. Further "the order 
of sequence in which the bivium comes in emphasizes family cha- 
racters.” The order I, V is characteristic of the Hemicidaridæ, 
Diadematidæ, Saleniidæ, Stomopneustidæ, Temnopleuridæ, Echinidæ 
and ""Strongylocentrotidæ”; the order V, I is characteristic of the 
Årbaciidæ and the Echinometridæ. On the other hand Jackson 
seems to me to go a little too far in stating that, because the 
genital plate 3 has been found divided by a transverse suture in 
275 instances, "this seems to be a family peculiarity, as it was 
observed in several species of the Echinidæ as in Tripneustes es- 
culentus and in the Strongylocentrotidæ” (p. 168). — I may here 
add the remark that the statement of Jackson (e.g. p. 88) that 
Salenia Pattersoni has no externally visible genital pores, is in- 
correct — of course. How should the animal get rid of its genital 
products, if there were no external genital pores? The pores are 
there, but are partly hidden among the prominences of the plates. 
