60 W. FELL WOODS ON THE RELATION OF 



being parasitic, the creature was a larval form of the Cockle ; and, 

 accordingly, from time to time, I exhibited it under that designa- 

 tion. Of course I may be altogether wrong in my interpretations, 

 and may but exemplify the truth of the proverbial expression that 

 " first impressions are always the best ;" but if so, I may probably 

 by this paper assist in guarding some other observer against 

 similar error. 



The reasons for my opinion were these : I found five prominent 

 states of the area occupied by the reproductive gland ; the first re- 

 vealed bunches of lobules containing spermatozoa 5 and possibly 

 ovules ; the second, similar bunches of lobules filled with well-defined 

 eggs, 6 which exhibited each its capsule affording a zona pellucida 

 around a membrane containing a mass of vitellus, within which was 

 a germinal vesicle with so-called spot. There might be indications 

 sometimes of a change in the latter, and also in the vitellus, but I 

 never found in the sacs an egg segmented. This being so, and 

 further never seeing any appearance of emptied sacs, pointing to 

 a discharge of the eggs, the third state of the Cockle was now 

 examined as to its possible connection with the two former. This 

 third state was that which displayed the developed tube, sometimes 

 containing only or mainly spherical masses of cellular structure in 

 a membrane, at others several or all of the stages up to the fully 

 developed Bucephalus! 1 It must, however, be noted that, whilst 

 many of the masses answered in size to what the eggs of a Cockle 

 should be when segmented, yet they were frequently so much less 

 opaque than I should expect that others could be seen through 

 them. 8 Yet a fourth state there was, 9 in which, besides the tube 

 with its contents, there were co-existent — sometimes, perhaps, in 

 the tube, but certainly in the ovisacs — full-sized eggs of the 

 Cockle. As a fifth state, I believe that on one occasion, 10 I found 

 in the tube, together with early forms of Bucephalus, the same 

 eggs as in the second state of the gland. Hence it seemed 

 highly probable that the spheres usually found in the tube 

 might be the segmented eggs, 11 whose continuous development up 



s April 19, 1873. April 25, 1873 (No. 5). May 2, 1873. April 18, 1874. 

 e April 14, 1873. April 16, 1873. 



7 June 14, 1872. February 18, 1873. March 21, 1873. April 29, 1873. May 

 20, 1873. May 27, 1873. 



8 February 18, 1873. April 29, 1873. December 9, 1874. Fig. B 2. 



9 July 4, 1872. April 16, 1873 (No. 2). April 29, 1873 (No. 3). May 9, 1873. 

 May 17, 1873 (No. 4). May 20, 187a 



i° April 16, 1873. 



11 March 21, 1873. May 9, 1873. May 12, 1873. Figs. H, J, and K. 



