ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
421 
Sphagnum , its endless bogs, and its immunity from drainage and 
reclamation. Notwithstanding Mr. Hood’s short experience, he is able 
to enumerate about 220 species, of which a considerable number are very 
rare. No species is here described as new, and only two, Pterodina 
hidentata and Eosphora elongata , are recorded for the first time as new to 
Britain. 
It will be remembered that about two years ago Miss Glascott 
published a catalogue of 158 species, 24 of which were new. With 
regard to these latter, however, it is probable that many are already 
"known forms. Making some allowance for duplication, the whole 
number of Rotifera of Ireland now reaches a total of about 275 species. 
Echinoderma. 
Development of Asterina gibbosa.* — Mr. E. W. MacBride has 
made, what was certainly wanted, a thorough revision of the whole 
history of the development of most organs of the starfish. Unfortunately, 
the student is so often referred from the text to the plates, that it is 
impossible in our space to make clear the body of the details which 
the author puts before us. On general subjects two main questions 
arise : what light does the developmental history of Asterina throw 
on the affinities of the Asterids with other Echinoderms, and does 
it suggest any direction in which we may look to find the origin of 
the group of Echinoderms as a whole. There can be no doubt that 
the stalks of Asterina and Antedon are morphologically equivalent. 
Both are formed from the pre-oral lobe, and the adhesive discs by 
which they fix themselves are situated in precisely the same posi- 
tion. Now no one doubts that Antedon had a fixed ancestor. If 
Asterids ever had an ancestor in common with Crinoids which could be 
called Echinoderms at all, it must have been one represented by the 
fixed larvae of Antedon before it had fully acquired radial symmetry. As 
the courses of the metamorphosis of Antedon and Asterina are different, 
the mouth shifting backwards in the former and downwards in the latter, 
the apparent correspondence of the calcareous plates of the calyx in 
Antedon and the so-called calyx in Asterina would appear to be due 
simply to the fact that their arrangement is in both cases dominated by 
prevailing pentamerous symmetry of the adult. This the student who 
is acquainted with the work that has been done on the morphology of 
the Echinoderms during the last twenty years will recognise as most 
revolutionary. It is not for that reason to be supposed that it is not 
justified by the facts that Mr. MacBride has collected. 
The author has done good service in insisting on the low character 
of the organisation of the starfish. He points out that there are no 
proper blood-vessels, no specialised excretory organ, a central nervous 
system which is really a local concentration of a diffuse skin plexus, 
perfectly simple generative ducts, and a most feeble development of the 
muscular system ; and lie asks, where is such a state of things to be 
found outside the Ccelentera? He insists that the almost complete 
atrophy of the ambulacral nervous system in the Crinoid, and its replace- 
ment by a new system developed in a totally different position, show 
* Quart. Journ. Micr. Sci., xxxviii. (1896) pp. 339-111 (12 pis.). 
1896 2 g 
