12 



0. SAES. 



[No. 7. 



connected with the preceding part of the body. Of any dorsal 

 projections in front of the tail for closing the matrix posteriorly, 

 there is no trace. Notwithstanding this, the incubatory cavity, 

 as in other Sididse, is pretty well deflued, partly by the body as 

 a rule lying in close contact with the dorsal part of the carapace 

 posteriorly, partly by a slight inner fold running on either side 

 along a somewhat curved line, more distinctly seen in specimens 

 whose matrix is greatly distended by numerous ova or embroys; 

 this line forms too the demarcation between the dorsal and 

 lateral, or more properly valvular, parts of the carapace. 



Inner Organs. — The cephalic ganglion (see fig. 1) is lo- 

 cated close to the ventral side of the head, in front of the la- 

 bium. As seen laterally it exhibits a somewhat oblique form, 

 the posterior part curving obliquely upwards to join the long com- 

 missures encompassing the oesophagus. From its inferior side 

 the two antennular nerves originate, whereas the nerves for the 

 antennae, as in other Cladocera, are given off from the oesopho- 

 geal commissures themselves. Immediately in front of the ce- 

 phalic ganglion the much smaller optic ganglion occurs, being 

 connected with the former by two very short commissures, which 

 may be distinctly traced, when the animal is viewed from below 



(see fig. 2); in the interspace between the commissures is seen 

 the ocellus imbedded within a clair projection issuing from the 

 cephalic ganglion. The optic nerves, as already noticed, are of 

 quite an extraordinary length and appear, when the animal is 

 viewed from below, pretty well defined from each other through- 

 out their entire length. 



The alimentary canal forms a simple cylindrical tube tra- 

 versing the body, and filled with a light greenish substance. 

 The part contained in the head curves slightly downwards, 

 becoming somewhat more roomy without however forming any 

 true coecal dilatations. The narrow, obliquely ascending oeso- 

 phagus joins the anterior part of the tube well-nigh at its ex- 

 tremity. Posteriorly the intestinal tube enters the tail, becoming 

 slightly dilated before joining the strongly muscular rectum, 

 which opens near the tip, just above the caudal claws. 



