314 SUMMARY OF CURRENT RESEARCHES RELATING TO 



this Cimpede. The points taken up are mainly anatomical, e.g. the 

 muscle systems, the digestive apparatus, and the circulation, though 

 some facts regarding its habits are also given. At Wood's Hole it is 

 found in large numbers, boring in Gastropod shells inhabited by hermit 

 crabs, of which it appears to be a regular messmate. 



Chilian Cirripeds.* — A. Gravel describes the structure of some 

 interesting operculate Cirripedia brought by L. Plate from Chili, namely 

 Coronuht diadema, Balanus psittacus, B. Jiosculus var. sordidus, CldJui- 

 malus cirratus, and G. scabrosus. 



Annulata. 



Mosaic Development in the Annelid Egg.f — E. B. Wilson records 

 certain interesting facts in the development of La/iice, having an 

 important bearing on this theory. When either cell of the two-celled 

 stage is destroyed, the remaining cell segments as if it still formed a part 

 of an entire embryo. The later development, however, is essentially 

 different. The posterior cell develops into a segmented larva with a 

 prototroch, an asymmetrical pre-trochal or head region, and a nearly 

 typical metameric seta-bearing trunk region, the active movements of 

 which show that the muscles are normally developed. The pre-trochal 

 or head region bears an apical organ, is more or less asymmetrical and 

 with only one eye. The anterior cell likewise yields a prototroch and a 

 pretrochal region, with an apical organ, but produces no post-trochal 

 region, develops no trunk or seta3, and does not become metameric. 

 This result shows that from the beginning of development the material 

 for the trunk region is mainly localised in the posterior cell ; and 

 furthermore, that this material is essential for the development of the 

 metameric structure. The opinion is expressed that, so far as the early 

 stages of development are concerned, it is difficult to escape the hypo- 

 thesis of formative stuffs or specific morphoplasmic substances, in some 

 form. The problem of the localising or form-determining factors which 

 are responsible for the determination of the segregation pattern remains, 

 however, unsolved. 



Ventral Sensory Organs of Palolo Worm.} — Olav Schroder 

 describes the peculiar structures which lie along the ventral median line 

 of Eunice viridis like so many pigment spots. There is a lens-like thick- 

 ening of the cuticle, there is pigment, there are sensory cells and 

 intermediate cells {ZicischenzeUen), but there is little to warrant the 

 view of Spengel, Hesse, and others, who regarded the organs as " eyes.' 1 

 The author notes how his results differ from those of Hesse, who 

 regarded Schroder's sensory cells as primitive nerve fibrils and Schroder's 

 intermediate cells as nerve-cells. 



Polynoid Commensal of Balanoglossus.§ — Ch. Gravier describes 

 Lepidasthenia digueti, sp. n., which lives as a commensal in the dorsal 



* Zool. Jahrb.,Supplementband vi., Fauna Chilensis, 1904, pp. 307-52 (3 pis.). 



t Science, xx. (1904) pp. 748-50. 



X Zt-itschr. -wiss. Zool., lxxix. (1905) pp. 132-49 (2 pis. and 2 figs.). 



§ Comptes Rendus, cxl. (1905) pp. 875-S. 



