188 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Dr. Zelinka has discovered the true ovaries, which lie close to the 
ventral and lateral wall of the beginning of the hind-gut. The mature 
ovum is relatively of enormous size, occupying a large part of the body- 
cavity, and crushing the gut and the other ova to the side. The mode 
of expulsion remains obscure. Like other observers, Zelinka failed to 
discover the summer-ova described by Metschnikoff. The laid eggs are 
ellipsoidal ; the embryo lies bent within the shell, and when mature 
bursts it by main force. The sexes are probably united, but the organ 
described by Ludwig as testis cannot be certainly regarded as such. 
Echinodermata. 
Ludwig’s Echinodermata.* — Prof. H. Ludwig continues and con- 
cludes his account of the water- vascular system of Holothurians ; he 
points out that the contents of the vessels are in no way identical with 
water, and that they contain a small admixture of coagulable albuminoid 
materials ; in a few cases the fluid is coloured, and cells are to be found 
in it. The digestive organs are next considered under the heads of 
(1) mouth and oral region ; (2) anus and anal region ; (3) divisions of 
the enteric tube and its macroscopical structure ; (4) histology of the 
tube ; (5) the course of the tube in the body-cavity ; this is rendered 
more intelligible than it is often found by the aid of three explanatory 
diagrams ; and (6) attachments of the enteron. The arborescent gills 
are next described ; the presence of more than two trees is merely due 
to the basal separation of a stronger branch ; an account is given of the 
minute structure of these organs. The part before us concludes with 
the early pages of the description of the interesting Cuvierian organs. 
Revision of Genera and Great Groups of Echinoidea.t — Prof. P. 
Martin Duncan has performed a very useful work in revising the genera 
and great groups, fossil as well as recent, of Echinoidea. Six divisions, 
two hundred and fifty-five genera, and fifty subgenera are recognized ; 
of these twelve genera and seven subgenera are new. One hundred 
and eight genera are regarded as synonymous with recognized types and 
abolished, and forty-two are made subgenera. Two subclasses are 
formed — that of the Palseechinoidea, all the members of which are 
extinct, contains four orders — the Bothriocidaroida, the Perischoechi- 
noida, the Plesiocidaroida, and the Cystocidaroida ; the two last are 
represented respectively by Tiarecliinus and EcJiinocystites ; the Euechi- 
noidea contains five orders, the Cidaroida, the Diadematoida, the 
Holectypoida, the Clypeastroida, and the Spatangoida. The Diadema- 
toida are divided into those with flexible and those with Arm tests ; 
the former, or Streptosomata, contains the single family Echinothuri[i]d8B, 
with the two subfamilies Pelanechinee and Echinothuri[i]n3e, but in an 
addendum, the author expresses his opinion that Prof. Jeffrey Bell’s 
account of the characters of Phormosoma requires the formation of a new 
subfamily for that genus, as distinguished from Asthenosoma ; the second 
suborder, that of the Stereosomata, contains a large number of families 
and subfamilies, Salenia, Diadema, Arhacia^ Temnopleurus, Echinometra, 
* Bronn’s Klassen u. Ordnungen, ii. 3, Echinodermata, 1889, pp. 129-76 (pis. 
vi.-viii.). 
t Journ. Linn. Soc., xxiii. (1889) pp. 1-311. 
