Miscellaneous. 381 



eye. Nevertheless traces of a primitive division into two halves in the 

 Sidce, the Lyncei, and the Estherios enable us to establish unhesi- 

 tatingly the homology of this apparently single eye of the Cladocera 

 with the paired eyes of the Cypridince. A further homology is 

 presented when we find in the Cypridince, besides the large com- 

 pound eyes, a small, simple, median eye, perfectly similar to that 

 which exists, in addition to the compound eye, in the DaphnicB. 



The Cypridin<s present other peculiarities worthy of mention. 

 As a general rule, the Ostracoda are characterized by the small 

 number of their appendages, as there exist only two, or at most 

 three, pairs of locomotive appendages behind the gigantic maxillae. 

 In fact, the last pair of feet disappears completely, and the others 

 are converted into organs of manducation. On the other hand, the 

 mandibles are converted into locomotive appendages. The antennae 

 also serving for locomotion, we find that throughout their whole life 

 the Cypridince employ the three anterior pairs of appendages as 

 locomotive organs. Now this is exactly the case in all Entomostraca 

 during the iVaz</)/zM«-phase, and furnishes a new argument to be 

 added to those adduced by Fritz Miiller in favour of the derivation 

 of all Crustacea from the Nauplius-iovm. — Siebold ^ Kolliker's 

 Zeitschrift, 1865, p. 143. 



Remarks on the Anatomy ©/"Tridacna elongata. 

 By M. Leon Vaillant. 



Tridacna elongata, Lam., occurs very abundantly in the Bay of 

 Suez, where it is often employed as food ; the author has accordingly 

 been able to examine a great number of individuals of this animal. 



The retractor muscle of the foot, which is of considerable size in 

 proportion to the protractor, serves in part for the closure of the 

 valves ; hence it may be that in those Monomyary Acephala which 

 have an adductor muscle distinctly divided into two parts, the upper 

 portion is to be regarded as representing the retractor of the foot 

 diverted from its normal functions. The byssus of the Tridacna, 

 already described by Miiller, consists of two parts — one adhering to 

 the bottom of a cavity of the foot, the other uniting this with ex- 

 ternal bodies ; each of these is secreted by a distinct organ, — the 

 former by the bottom of its cavity, the latter by a collection of 

 racemose glands lining a circular groove in the wall of the cavity. 



The large notches of the margins of the shells enabled the author 

 to ascertain the force which the mollusk is capable of exerting. He 

 fixed an individual by one of its valves, and suspended a weight to 

 the other. In this way he found that a specimen 21 centimetres in 

 length, of which the valves weighed 1-264 kil., could support a 

 weight of 4-914 kil. ; so that it may be supposed that an individual 

 weighing 250 kilogrammes (and these are not uncommon) might at 

 a given moment put out a force of more than 900 kilogrammes. 



In the nervous system the branchial ganglia, forming a single mass 

 with no trace of longitudinal division, exhibit transverse furrows 

 bounding two false circumvolutions. A sort of inelastic tendon 



