124 



HARD WICKE' S S CIENCE- G OS SIP. 



white band, often found running with No. 3, I do 

 not know ; but such is probably the case. 



A shell of rubella oo 34 o from St. Mary Cray is 

 unusually thin, and is of a light pinkish yellow or 

 flesh colour. 



(2.) Shell orange colour. This might be called 

 aurantia. I have only taken a bandless form, which 

 is fairly common on a bank at Crayford. 



T. D. A. COCKERELL. 



August, 1885. 



ON THE DEVELOPMENT OF THE TAD- 

 POLES OF THE COMMON FROG {RANA 

 TEMPORARIA). 



IN Science-Gossip, Vol. XVII. p. 59, there is an 

 interesting article on frog-spawn and its develop- 

 ment by M. H. Robson, Hon. Sec, North of England 

 Microscopical Society. As he has so recently given 



external gills (branchiae) disappeared ; 22nd, all 

 took to floating on their backs, and continued to do 

 so for some days. I could see their viscera as shown 

 in Fig. 75. 23rd, viscera as shown in Fig. 76. I could 

 see that their bodies were beautifully splashed with 

 golden colour. Up till the 23rd those in the shallow 

 vessel had kept pace in growth with those in the fish- 

 globe, after then they did not increase either in 

 length or breadth for a fortnight, at the expiration of 

 which time I removed them into a vessel containing 

 about three times the quantity of water, with more 

 weed, for, although I wanted to keep them back, I 

 did not wish them to die. They immediately made a 

 fresh start, but never grew or developed so quickly as 

 those in the fish-globe, so that when those in the last- 

 named vessel had become lung-breathing batrachians, 

 which some did as early as May 26th, and the last of 

 that lot by the middle of June, I removed those in 

 the smaller vessel into the fish-globe, and they did 

 not fully develop until the end of August ; these later 



Fig. 75. — Tadpole, twelfth day (much enlarged). 



Fig. 76. — Tadpole, thirteenth day (much enlarged). 



us remarks, accompanied with plates, on the first 

 stages of its development, I shall not dwell particu- 

 larly on this portion of the subject, only sufficiently 

 to show the difference in the time of development, 

 owing to difference of temperature. 



On March nth, 1881, I procured some frog- 

 spawn, and placed some of it in a fish-globe con- 

 taining river water and aquatic plants, principally 

 Anacharis Canadensis and tiitella, and a smaller 

 quantity of the spawn I placed in a shallow vessel 

 containing about a pint and a-half of water and some 

 Anacharis. The two vessels were kept in a room 

 with a fire in it all day, and the aspect south-east. 



Now if you will compare M. H. Robson's account 

 with mine, you will see the difference of time in the 

 development. 



March 1 ith, in situ. 13th, cleavage or segmentation 

 of eggs ; 14th, much larger ; began to move and turn 

 their heads and tails together in their efforts to free 

 themselves from the gelatinous egg mass which sur- 

 rounded them ; 18th, tadpoles had emerged ; 21st, 



ones grew to be much larger as tadpoles (also as frogs) 

 than the earlier ones. I found it very interesting to 

 examine them under the microscope. They can be 

 easily kept quiet by adopting M. H. Robson's plan, 

 or when quite small one can be placed in a cell, but 

 it should not be left to remain in there longer than 

 necessary for examination, or it will die. I had one 

 in a cell one evening, and left it until the following 

 evening, when on placing it under the microscope, to 

 examine its branchiae, I found the circulation had 

 quite ceased in that on one side of the head, but was 

 flowing rapidly in the opposite one. I judged it was 

 dying, and such was the case, for it immediately 

 expired. I was much vexed to think that through 

 my thoughtlessness the little creature had died. 



I used to watch their movements with much 

 interest, and speculate on the causes which affected 

 their actions. I found light, temperature and aliment 

 had much to do with them. On dull cold days the 

 tadpoles would be seen at the lower part of the vessel, 

 moving about slowly, and even hiding under the stones 



