NOTES AND CORRESPONDENCE. 
Zoosperms in the Ovaria of Pulmoniferous Gastropods.—In 
the April number of your Journal I find a communication 
regarding tlie above subject, from one of your correspondents. 
In this communication the writer impugns the accuracy of 
my assertion, that the zoosperms are not secreted in the 
ovary properly so called. It is stated that, because the 
structures in question are to be seen in a fully developed 
condition in the saccules of the ovary, the latter organ is 
that which gives them birth. Now, without desiring to 
dwell upon the fact that the petitio principii is hardly a fair 
mode of reasoning, allow me to indicate to your corre- 
spondent a few of the difficulties which his assumption 
involves. 
lst.—The zoosperms being found fully developed in the 
ovary and imperfectly formed [spermatophora] in the sperm- 
sac, they must, according to his hypothesis, have undergone 
a species of retrograde development. 
2nd.~-There being but one oviduct, the zoosperms must 
pass out with the ova, and, therefore, be utterly valueless so 
far as reciprocal fecundation is concerned. 
3rd.—The testis [mihi] which is tout entier of greater 
volume than the ovarium, would have but a subordinate 
function attached to it. 
4th.—It would be impossible to show how the zoosperms 
pass into the spermatheca.— Henry Lawson, M.D., Professor 
of Physiology im Queen’s College, Birmingham. 
Stereoscopic Photographs of Diatoms,—At the recent soirée 
of the Microscopic Society were exhibited a series of photo- 
graphs; by Dr. Maddox, of various forms of Diatomacee, in 
which the markings were defined with great distinctness, and 
the peculiar appearances produced with differences of illumi- 
nation were illustrated. ‘These attracted considerable notice. 
