Onr Fresili-xoaier Eiitomostmca — Chambers. 25 



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a single specimen of a small mussel, so like it in size and form that I 

 was not convinced of the difference until I took it in my fingers. But 

 the mussel shell is hard and calcareous, while that of the Edheria is 

 thin, flexible and chitchitnous. It is attached to the body of the animal 

 just behind its head, and is composed of a series of concentric laminse 

 or rings, which Dr. Baird supposed to represent each an annual growth. 

 But his conclusion may perhaps be doubted. In the specimen taken 

 b}- me I counted thirty-five such rings, and it is almost incredible that 

 this defenseless little creature had successfully weathered all the vicis- 

 situdes of pond-life for thirty -five years. Estheria swims by jerking itself 

 along through the water with its long antennae, aided by motions of the 

 abdomen, making, as it were, a series of successive jumps, and resem- 

 bling rather the jerking motions of Daphrua than the gentle and grace- 

 ful undulations of Branchippus. The young, also, atone stage, bear 

 some resemblance to some adult Daphnke, as, however, those of Bran- 

 chippus and Chirocephalus likewise do ; the resemblance, however, is 

 not very close. The specimen taken by me carried a saddle of eggs 

 across the back, just behind the point of attachment to the shell. The 

 eggs were very numerous, some hundreds I should say, though I did 

 not count them, very small, globular, and pale yellow. The specimen 

 died from injury received in handling it, and only four of the eggs 

 hatched, and all of these died before the third month. I regretted 

 tins the more, because if its development has been heretofore observed, 

 I am not aware of it, and I was anxious to trace its course. All the Fhil- 

 lopocla undergo metamorphosis, and Estheria is no exception to the rule. 

 In its first or Nauplius stage, just emerged from the egg, it closely resem- 

 bles Dr. Baird's figure (Nat. His. Brit. Ent., plate 5) of Chirocephalus 

 diaphanous at the same age, but it is even a more simple and elementary 

 form (approaching somewhat to the young of Cyclops). The projecting 

 antennse of Dr. Baird's figures are represented by SetJB only ; the pos- 

 terior pair of limbs is not so much developed, and the thorax is less 

 distinct from the abdomen, which is notched at the apex. It was first 

 observed at 3 p. m., and at 9 p. m. the only change observed was that 

 the limbs were more distinct, and had a more definite outline ; the tho- 

 rax was more distinct from the abdomen, the apex of which was dis- 

 tinctly furcate. At 9 a. m.- next day the projecting points at the apex 

 of the abdomen (post abdomen) were much better developed, the 

 limbs, thorax and abdomen were very distinct from each other ; the 

 branchiae were rudimentary, and a shield (the beginning of the shell) 

 covered the head and thorax above, and a similar, but smaller shield, 

 attached only by its anterior margin, covered the ventral surface of 

 the thorax. 



The next family in the arrangement of Prof. Rupert Jones, which I 



