Holt — On the Eggs and Larvce of Teleosteans. 453 



A single egg (fig. 14) apparently belonging to this species, with diameter 1-31, 

 and oil-globule "21 mm., occurred in the surface-net in Clew Bay on the 2nd 

 July. 



The zona in this specimen exhibits nothing of special interest ; the perivitelline 

 space is small ; the embryo is little advanced, with about four protovertebree : no 

 pigment is present; the oil-globule has migrated a short distance towards the 

 posterior region. 



Pleuronectes microcephalus (Donov.). The Lemon Dab, or Lemon Sole. 

 PI. XLViii., figs. 19-21 ; PI. L., fig. 39. 



Ripe females were obtained frequently, yielding an abundance of mature ova. 

 Some which I measured on the 25th June had a diameter of r25 mm.,* being thus 

 smaller than those measured by Mr. Cunningham, at Plymouth| (op. cit., p. 15). 

 I endeavoured to fertilize these, but without success. Four hours later they were 

 still translucent and floated buoyantly, whilst in a few a small perivitelline space 

 had appeared, as after fertilization. 



Cunningham [ibid.) points out that " the external surface of the vitelline mem- 

 brane shows a number of fine raised ridges forming two systems of parallel lines 

 which cross one another diagonally." M'Intosh and Prince give a figure {op. cit., 

 PI. I., fig. 18) of part of the zona under a high power, showing a somewhat 

 irregular reticulation of lines, seen as white spaces on the closely dotted surface. 

 The latter condition is more in accordance with my own observations. Examina- 

 tion of the zona in the living egg (fig. 21) certainly gives the impression described 

 by Cunningham, but if it is ruptured and flattened out, it is seen (fig. 20) that the 

 markings are extremely irregular. There are certainly two general systems of 

 parallel lines, but these lines are by no means continuous, frequently ending 

 blindly, converging and diverging, or bending abruptly to continue their course 

 at a different level. Seen from above the markings appear as a line on to which 

 the thickly-set punctures of the rest of the zona do not extend. By tracing the 

 lines to a point where the zona is doubled over so as to present an optical section, 

 it is clearly seen that they are not ridges at all, but sharp grooves indenting the 

 surface of the zona from about a quarter to a half of its thickness, according to 

 the size of the lines, which are of varying widths. In some instances the sides of 

 the grooves are very slightly raised above the general surface level. 



By the kindness of Professor M'Intosh I have been enabled to add to my 



* Some dead fertilized ova of this species in the tanks here measured from 1'2 to 1'31 mm. 

 f Mr. Cunningham gives 1-36 to 1-44 mm., "though individual ova may be a little smaller or a little 

 larger." In an earlier paper he gives 1-1 mm. as the diameter of the mature (unfertilized) ovum. 



3 S2 



