222 GENERATION 



armed with spikes like a crab 1 . These breed by laying their eggs round 

 that opening where the excrements are discharged, and where the water 

 is drawn into the gills, and are there hatched, about fifty or sixty in 

 number. They may be pinched off, being about the size of small pins' 

 heads ; and by viewing them with a microscope, they may be distinctly 

 seen in their different stages, from the ovum to the complete animal 

 (preparations of them in their attachment and adult form). [Quaere: 

 Where?— Wm. Clifx.] 



Generation of the Oyster [ Ostrea edulis] . 



The mode of generation in the oyster, mussel, <fec, has not been in 

 the least known, which has been from the want of appearance of parts 

 of generation [in them]. But I have taken notice in the oyster that 

 there is a great difference of appearance in the animal at different times 

 of the year. In the winter they appear full or fleshy, by a thick white 

 soft glandular part covering the stomach, liver, and intestines. This 

 part seems to be made up of vessels branching like veins over the 

 liver, and those branches open by two small orifices into that passage 

 leading to the inside of the gill, on each side of that projecting part 

 made by a doubling of the intestine ; and at these openings the con- 

 tents may be squeezed out, which in the winter contain a milky fluid, 

 or rather like cream, but not so high-coloured ; and at this time, when 

 viewed in a microscope, [the contents] appear of a uniform texture. 

 But in June I observed that they were becoming smaller, that is to 

 say, the gland was decreasing. I squeezed the matter out, observing 

 that it was more viscid ; and on diluting it with water, and viewing it 

 with a microscope, there evidently appeared small ova in it, pretty well 

 determined [in shape] and nearly equal [to one another] in size. 



This happened to be in the beginning of July, and now they [the 

 oysters] were becoming very thin. On opening one, I observed a pur- 

 plish granulated appearance like very fine sand in the gills, [with] in 

 the shell ; and on viewing it in the microscope, they appeared to be 

 oysters formed with their shell, and by their transparency I could see 

 the embryo of the oyster ; but I never could get them so far advanced 

 in the ovarium. 



After this, at the Isle of Wight, I found several where the ovarium 

 was decreasing ; and on squeezing out the contents, I observed the ova 

 more distinctly than I had ever [before] seen them. 



1 [Acanthoscelis, ' Lectures on Invertebrate Animals,' p. 525. The true embryo 

 of Anodon has a hooked apex and spines on the shell, and was supposed to be a 

 parasite by Rathke. who described it under the name of Glochidium.] 



