2 
The Embryology of Patella. 
A very small amount of acetic acid is sufücient to kill tlie 
embryos instantly; tliey bowever retain theircolor and unless 
placed in glycerine at once, dissolve or fly to pieces in a very 
remarkable manner. If tlie acetic acid is too strong tbe ova 
become too transparent and the cells lose their sbarp outlines. 
One drawback to tbe nse of acetic acid is tbat it is liable to lead 
one into error unless supplementary studies aremadeupon material 
wbicb bas been prepared in otber ways. The cilia of tbe velum 
for example are well preserved by acetic acid and thus one is 
led to suppose that if tbere were other cilia present they would 
be equally well perserved, but tbat is not tbe case. For tbe 
bunch of large and prominent cilia situated at tbe animal pole, 
and the long stiff bairs of tbe anal cells disappear like a flasb 
on the addition of acetic acid and not a trace of them is to be 
observed upon the otherwise well preserved embryos. These large 
“cilia may be studied in tbe living embryos or by examining pre- 
parations made in osmic acid and glycerine, as in these media 
all tbe cilia are well preserved. 
Tbe sections represented in tbe plates were all drawn witb 
tbe aid of the camera and cut from embryos killed in acetic acid, 
preserved for some time in alcohol and afterwards stained either 
in alcobolic borax carmine or Kleinenberg’s baematoxylin. 
A great many embryos were preserved in osmic acid and 
otbers in Sublimate, or a mixture of Sublimate and picric acid. In 
tbe last two cases it was difficult to make tbe embryos trans¬ 
parent by means of acetic acid and glycerine, although tbis could 
be done quite easily when the embryos bad been originally killed 
in acetic acid. 
No sections were made of embryos prepared either in osmic 
acid or Sublimate, as tbose killed in acetic acid could be stained 
and sectioned witb entire satisfaction. 
II. Fecundation of the ova. 
After many unsuccessful attempts to obtain tbe ova of 
Haliotis, Fissurelia and Patella, during wbicb my attention was 
called to tbe absence of any external sexual organs or albuminous 
gland to furnish envelopes for tbe ova, I came to tbe conclusion 
tbat tbe ova were scattered about singly in tbe water and tbere 
underwent an external fecundation. 
(150) 
