1^6 BEV. T. RIDDELL ON THE BALANUS. 



Treed. In the course of the day (14th June) I sketched several figures 

 with pen and ink ; the annexed (Figs, a and h) are a side and back 

 view. Under a high magnifier the skin which covers the globules 

 (near the blunt end) has a granulated appearance. 



On the following morning, when I examined the saucer containing 

 the animals, I was surprised to see some of the eggs (as I had supposed 

 them) moving swiftly about and swimming through the water. When I 

 had taken one out and placed it in a hollow glass under the microscope, 

 the rapidity of its movements was such as to prevent my examining 

 it ; shortly afterwards it was seen to move more leisurely along the 

 bottom of the glass, putting forth a sort of tongue which it fixed on the 

 glass in front of itself, and then retracted so as to draw itself forward* 

 My first thought was, this is evidently an entomostracous animal, a 

 C}^ris or something similar ; but having a small creature of that kind 

 (some species of cythera probably) under the microscope at the same 

 time, there appeared a marked difference between them, the limbs of 

 the latter being evidently much more perfect. 



In the course of the day having obtained a loan of Mr Thomj)son's 

 work, I was enabled to compare his figures with my own observations. 



Respecting Fig. 1, Plate IX. which is intended to represent the natu- 

 ral size of the young animal, it must be observed that this is fuU twice 

 as long as it ought to be, and more than twice as broad. This remark 

 is not so unimportant as it may at first appear. The size of the 

 young Balanus, as given by Mr T., has been alleged as a strong 

 argument against the correctness of his views, because perfect animals 

 are frequently found much smaller. Perhaps the enlargement of a 

 minute figure in the process of copying and engraving is not uncommon. 



Fig. 2 represents an indentation at the top of the case, corresponding 

 to the cleft in the animal. This has not been observed either by Dr 

 Johnston or myself. 



The annexed figure (Fig. c.) answers to Mr T.'s 3d figure. The 

 eye (Fig. 4.) I did not see ; of the tail I have only seen the two long 

 bristles, which are much longer than in Mr T.'s drawing. Fig. 6 I 

 have not been able to verify, but I have no reason to judge it other- 

 wise than correct. 



As yet I have not been so fortunate as to ascertain the actual change 

 of the above animal into a Balanus ; but the circumstances of their 

 being found together, and the great similarity between the Balanus 



