386 SUMMARY OF CURRENT RESEARCHES RELATING TO 



visible at certain periods and by special methods. The details of the 

 structure and its changes are described. But the main point is that 

 the monosome is a genuine chromosome, and has the same characteristic 

 structure. 



f- Crustacea. 



Ova and Vitelline Cells in Entomostraca.* — Y. Willem and L. de 

 Winter point out that Crustaceans show a variety of modes of ovum- 

 nutrition, analogous to the variety that obtains in Insects. In one of 

 the Copepods, Doropygus {Notopterophorus) gWher Thor., there is a con- 

 dition similar to the mero'istic ovary of Collembola, for abortive ova are 

 used for the nutrition of the successful ova. In other cases (such as 

 Cyclops, Canthocamptus, Diaptomus) all the oogonia may become ova ; 

 the ovary is panoistic, as in many insects. In the water-beetle, Dytiscus^ 

 the oogonia exhibit a differential division, which results in a lineage of 

 ova and a lineage of nutritive cells. The same sort of meroistic ovary 

 has been observed in Cypris and other types. 



Memoir on Hermit-crab.t — W. Gordon Jackson gives an account 

 of Ewpagurus heiiihardus^ including the minute structure of the gut 

 and digestive gland, the complex excretory system (with arborizations 

 in the cephalothorax and a large abdominal sac), the eye and otocyst, 

 and so on. He deals also with the gonads, the sex-cells, and the six 

 larval stages — four Zosea stages, a Glaucothoe, and an adolescent stage. 

 A very interesting account is given of the ecology of the hermit-crabs. 



Tubicolous Idotheid.J — R. Issel gives an interesting account of, 

 Zenohiana prismatica (Risso), a small Idotheid which lives inside pieces 

 of stem (Zostera) or rootlet {Posidonia), and the like. The peculiarities 

 of habit in relation to the tubicolous mode of life are discussed. 



Annulata. 



Changes of Musculature in Sexually-mature Nereis fucata.§ 

 H. Charrier finds that in the male " Heteronereis " the muscles thicken 

 greatly. In the epitokous forms each of the large longitudinal dorsal 

 muscles forms a longitudinal fold which projects into the coelom. But 

 in addition to the change of size and form, there is a remarkable and 

 intimate change in the minute structure. This change differs con- 

 siderably in different parts, and is carefully described. 



Formation of Setae in Polych8ets.|| — G. Pruvot has studied this in 

 Perinereis cidtrifera. The secretion of the substance of the seta3 is due 

 to setigerous cilia borne by the mother-cell or chaetoblast. The longi- 

 tudinal striae, which give the seta a fibrillar appearance, are traces of 

 the retreat of the cilia as the seta elongates. The cilia in question are 



* Bull. Classe Sci. Acad. Roy. Belgique, 1913, No. 3, pp. 204-10 (1 fig.)- 



t Liverpool Marine Biol. Committee, Memoir xxi. (1913) pp. 1-79 (6 pis.). 



X Arch. Zool. Exper., li. (1912) pp. 479-500 (6 figs.). 



§ Comptes Rendus, clvi. (1913) pp. 1331-2. 



II R6sum6s des Communications, 9e Congres Zool. Monaco (1913) ser 2, p. 11. 



