300 EVENINGS AT THE MICROSCOPE. 



Among the multitude of transparent creatures that swim 

 in the open sea, few are more interesting than the infant 

 state of the very animals that we have lately been examin- 

 ing ; the Sea-Urchins and their allies. It is a productive 

 way of obtaining subjects for microscopic research, to go 

 out in a boat on a quiet summer's day, especially in the 

 afternoon, when the sun has been shining, or when even- 

 ing is waning into night, and, with a fine muslin net 

 stretched over a brass ring at the end of a pole, skim the 

 surface of the smooth sea. At intervals you take-in your 

 net, and having a wide-mouthed glass jar ready, nearly 

 filled with sea-water, invert the muslin in it, when your 

 captures, small and great, float off in the receiver. After 

 a few such essays, unless you have very bad success in- 

 deed, you will see even with the naked eye, but much 

 more with a lens, that the water in your jar is teeming 



form us that two species of Synapta are found in the British seas, one 

 of which, the Chirodota digitata of B. Forbes, is the species referred to 

 in the text as being in ray own possession. Its Bkin proves to be studded 

 with anchors, not with wheels, and it is on this ground referred to the 

 genus Synapta. 



Still later (See Qu. Jowrn. Micr. Sri. for 1862, p. 131), Dr. Wyville 

 Thompson has obtained Synapta inhcerens in the Irish Loughs of Belfast 

 and Strangford. In his admirable paper on the infancy and develop- 

 ment of this curious creature, elaborately illustrated, he has traced the 

 gradual formation of the calcareous spicnlse, from their first indication. 

 The anchor first appears as a straight rod sharp at both ends. One end 

 gradually becomes knobbed ; the knob extends on each side, giving the 

 rod a T form ; and soon the arms curve backward, giving the anchor- 

 form. Then the basal end becomes dilated. Hitherto no trace of the 

 plate has appeared ; but now a small glassy needle is seen lying across 

 the shank near the base. Each extremity of this now branches, and 

 these again branch, the points meeting and uniting here and there, 

 until at length the plate is gradually mapped out. As yet the openings 

 left by the uniting network are smooth-edged ; but the glassy network 

 gradually strengthens, and the edges of the holes, now no longer meshes 

 of a net, but orifices in a plate, are studded with teeth all round. I 

 refer my readers, for much information of the deepest interest, to this 

 very valuable memoir. 



