386 OILMAN A. DREW. 



cardial openings ai'e hard to find. The outer end of each 

 excretory organ opens into the mantle chamber, in connec- 

 tion with the genital duct of the same side. (See pp. 380, 381.) 



Genital Organs. — The genital oi'gans are formed after 

 the animal is adult in most other respects. They can first be 

 distinguished as short tubes that lie very close to, or in 

 contact with, the pericardium, and open into the mantle 

 chamber in connection with the outer ends of the kidneys. 

 The genital organs become very extensive in the adult. The 

 sexes are separate. (See pp. 381, 382.) 



Most of the work necessary for the preparation of this 

 paper was done in the Biological Laboratory of the Johns 

 Hopkins University. To many that are now or formerly 

 were connected with that laboratory, and especially to Pro- 

 fessor W. K. Brooks, I am indebted for suggestions and 

 encouragement. I also desire to express my appreciation of 

 the courtesies extended to me by Professor C. O. Whitman, 

 at the Marine Biological Laboratory. I am particularly 

 indebted to my wife, who has, among other things, performed 

 a great share of the work connected with the care and pre- 

 servation of material. Beside the work at the sea-shore, 

 embryos obtained in June were kept alive in Baltimore from 

 October 1st until January 1st, with vvatei- sent from the sea. 



LiTEEATUEE. 



1. Drew. — "Yoldia limatula," 'Memoirs from the Biol. Lab. of ilie 



Johns Hopkins Univ./ vol. iv, No. 3, 1899. 



2. Drew. — " Some Observations on the Habits, Anatomy, and Embryology 



of Members of the Protobranchia," * Anat. Adz.,' Bd. xv, No. 24, 

 1899. 



3. Drew. — "Locomotion in Solenomya and its Relatives," 'Anat. Anz.,' 



Bd. xvii. No. 15, 1900. 



4. Forbes anb Hanlby. — 'History of British MoUusca and their Shells,' 



1853. 



5. Grobben. — " Die Pericardialdriise der Lamellibranchiaten," ' Arb. 



Zool. Inst. Wien,' Bd. vii, 1888. 



6. Jackson. — "Pliylogeny of the Pelecypoda," 'Mem. Boston Soc. Nat. 



Hist.,' vol. iv, No. 8, 1890. 



