300 
ON THE RENAL ORGANS OF NUCULA NUCLEUS, Lixn. 
By R. H. Busgne, B.A., F.Z.8., etc. 
Read 9th January, 1903. 
PLATE X. 
Tar anatomy of many members of the Protobranchia has been in- 
vestigated with considerable care during the last ten years, and has 
been found to show in many points indications of the retention in 
these forms of a very primitive and unspecialized condition. 
Amongst the organs distinguished by primitive characteristics are 
the organs of Bojanus, and they, especially in their relations with the 
genital ducts, are without doubt of very great interest. In 1891 
Pelseneer' drew attention to the fact that in Mucula nucleus, Leda 
pella, and Solenomya togata the genital duct communicated with the 
exterior through the organ of Bojanus, opening into that organ, not, 
as it does in several other lamellibranchs of a low type, just within 
the external orifice, but close to the pericardium. The importance of 
this announcement is obvious, for this arrangement points towards 
a yet earlier stage in the specialization of the lamellibranch cxelom, 
in which the genital, pericardiac, and renal celomic cavities were in 
open communication, and the genital products escaped, as they now do 
in Aplacophora, through the pericardium and nephridia—a stage but 
httle in advance of the condition characteristic of Annelids, in which 
the genital products are formed at certain points upon the walls of 
a general cxelomic cavity, and escape from that cavity through peritoneal 
funnels comparable to the Molluscan kidney. This observation was 
later on confirmed by Stempell,* so tar as concerns Solenomya, but 
apparently the lke condition does not occur in the members of the 
Nuculide and Ledidee examined by him‘ or by Drew.’ For instance, 
1 P. Pelseneer, ‘‘ Contribution 4 |’étude des Lamellibranches’’: Arch. de Biol., 
tom. xi (1891), p. 165. 
2 Goodrich, ‘* On the Ceelom, Genital Ducts, and Nephridia’’: Quart. Journ. Micro. 
Sci., vol. xxxvii (1895), p. 477. 
3 Stempell, ‘‘ Zur Anatomie von Solenomya togata, Poli’’: Zool. Jahrb., Bd. xiii 
(1900), p. 141. 
4 Stempell, ‘‘ Beitrage zur Kenntniss der Nuculiden’’?: Zool. Jahrb. (Fauna 
Chilensis), Bd. i (1898), p. 398. 
5 Drew, ‘‘ Some Observations on the Habits, Anatomy, and Embryology of members 
of the Protobranchia’’: Anat. Anz., Bd. xv (1899), p. 503. ‘‘The Life- 
History of Nuenla delphinodonta (Mighels) ”: Quart. Journ. Micro. Sci., vol. xliv 
(19J1), p. 380. 
