56 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Fresh-water Nereids.* — H. P. Johnston gives an account of three 

 undescribed species of fresh-water Polychsets, all belonging to the family 

 Nereidse. All three species live in perfectly fresh (drinkable) water — 

 Nereis lemnicola sp. n., from Lake Merced (invaded by salt water in late 

 Quaternary times, but now part of the water system by which San 

 Francisco is supplied); Lycastis hawaiiensis sp. n., from a spring near 

 Honolulu ; and Lycastoides alticola g.et. sp. n., from the Sierra Laguna, 

 Lower California, an elevated habitat. 



The possibility of a marine animal establish ing itself in fresh-water 

 is determined by four essential factors, two of which are intrinsic and two 

 extrinsic : — 



1. The possession of euryhalinism, i.e., the power of enduring con- 

 siderable alterations in the salinity and specific gravity of the medium. 



'1. The presence of a suitable fresh-water habitat, accessible from the 

 sea, with intermediate brackish -water areas. 



3. The possibility of obtaining food in the new habitat. 



4. The capability of breeding in the new environment. 



Genital Ducts in Oligochaeta.t — YV. B. Benham describes a new 

 species, Haplotaiis heterogyne, which is provided with only a single pair 

 of ovaries and oviducts, and whose sperm-ducts and nephridia appear 

 to be structurally almost identical. While the sperm-funnel is ana- 

 tomically quite different from the nephridial funnel of the neighbour- 

 ing segments, the sperm-duct is practically indistinguishable from a 

 nephridial tube, and it originates from the funnel at the extreme ventral 

 margin, in the position in which a nephridial funnel, if it were present, 

 would lie. In other words, the duct does not issue from the centre of 

 the funnel as in the sperm-ducts of other Oligochajta. It is suggested 

 that here is a composite organ, such as Goodrich has described in several 

 Polychaeta, and termed by Lankester " nephromixium." It would appear 

 that the sperm-ducts are not absolutely homologous throughout the 

 Oligochreta. 



New Species of Genus Phreodrilus.J — W. B. Benham describes three 

 new species of this genus of Oligochasta from New Zealand. Their 

 characters are such as to support the view of Michaelsen, who includes 

 in this genus the Hesperodrili of Beddard. 



Urns of Sipunculus nudus.§ — F. Ladreyt finds that these "organites" 

 arise from the connective tissue of Poli's tubes and the covering endo- 

 thelium. They are not phagocytes, for no part of the material collected 

 by their cilia is to be found within the urn. It is thrown into the 

 ccelome. Their morphology and physiology exclude the hypothesis that 

 they are Protozoan or Mesozoan parasites. 



Embryonic Envelope of Sipunculids.|| — J. H. Gerould seeks to show 

 that the serosa of Sipunculus represents the remains of a degenerating 



* Mark Anniv. Vol., 1003, pp. 205-23 (2 pis.). 



t Quart. Journ. Micr. Sci.. xlviii. (1904) pp. 299-322 (3 pis.). 



t Tom. cit.. pp. 271-98 (3 pis.) 



§ Comptes Eendus, exxxix. (1904) pp. 370-1. 



|| Mark Anniv. Vol., 1903, pp. 437-52 (1 pi.). 





