206 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
paired eyes scarcely developed or sometimes absent in the most 
primitive family, well-developed and schizochroal in tbe last family. 
Includes tbe families Encrinuridae, Calymenidae, Cheiruridae, and 
Phacopidae. 
The Hypoparia probably culminated in the pre-Cambrian times, the 
Opisthoparia during the Cambrian, and the Proparia during the Ordo- 
vician. The Opisthoparia are represented by about 85 genera in the 
Cambrian, 45 in the Ordovician, 19 in the Silurian, 10 in the Devonian, 
4 in the Carboniferous, and 1 in the Permian. 
Annulata. 
Pelagic Larvae of Polychseta.* — Dr. Y. Haecker describes many of 
the pelagic larvae of Polychaeta which are to be found in spring in the 
Gulf of Naples. He distinguishes the trochophore (without hint of 
metameres), the metatrochophore (in which segments are beginning to 
be defined), the nectochaeta (with reduced ciliation, but with strong 
setose natatory appendages), and the protrochophore (without mouth or 
anus, with broad pre-oral zone bearing short cilia), a stage antecedent to 
or replacing the trochophore. 
After defining the various regions of the larval body, the author 
describes the larvae of the different families. 
The assumption of a pelagic stage is interpreted as an alternative to 
the acquisition of a store of yolk. Both are adaptations to secure the 
nutrition of the young. All possible transitions occur between those 
forms which become sedentary immediately after being hatched, and 
those which are from the first pelagic. 
The author distinguishes four groups : — I. Tubicolous forms with 
non-pelagic larvae (Terebellidae, Ariciidae, Arenicolidae (?) ; II. Tubi- 
colous forms with strictly pelagic larvae (Chaetopteridae, Spionidae, Ser- 
pulidae, Archiannelidae) ; III. Errantia without pelagic larvae (some 
Eunicidae and Syllidae) ; IV. Errantia with strictly pelagic larvae 
(Nephthyidae, Nereidae, Phyllodocidae, and Aphroditidae). 
Not the least important part of this valuable memoir is the third 
chapter, iu which the author discusses the comparative histology and 
physiology of the integument — the pigmentation, the primary sense- 
organs, the locomotor apparatus, the primary^glandular and skeletal tissue. 
Asymmetry of Spirorbis.j — MM. Maurice Caullery and F. Mesnil 
describe the asymmetry of Spirorbis induced by its habitat in the 
interior of a spiral tube. The direction of the turn of the spire is con- 
stant for a given species ; the operculum is always on the concave side ; 
the longitudinal muscle-fibres are strongest on the same concave side ; 
the viscera are thrown towards the same side ; the uncini on the thorax 
and abdomen are larger and more numerous on the concave side ; the 
ovules in course of maturation are always on the convex side ; and so on. 
All can be explained by the movements made by the animal within the 
tube. The authors distinguish right-handed and left-handed species, and 
in a detailed memoir (referred to) have applied the facts to a phyloge- 
netic consideration of the group. In a note on the above, Prof. E. Perrier £ 
directs attention to some previous observations which he made bearing 
* Zeitschr. f. wiss. Zool., Ixii. (1896) pp. 74-168 (3 pis., 8 figs.). 
t Ann. and Mag. Nat. Hist., xix. (1897) pp. 411-3. Comptes Rendus, cxxiv. 
jjp. 48, 50. % Tom. cit., pp. 50-1. 
