MOKPHOLOGY OF CYCLOPS. 25 



junction of the second and third ahdominal segments ; from which two muscles diverse, 

 the anterior heing a retractor and the posterior a protractor. Two muscles extend 

 backwards from the anterior edge of the fourth segment, and are inserted into the upper 

 wall of the rectum just before the anus; they would protract the rectum and dilate the 

 anus at the same time. Besides these, on the ventral side a sheet of tine fibres passes 

 from the anterior end of the fourth segment upwards and backwards on to the rectum, 

 and acts at once as retractor and dilator. 



Lateral Muscles. — A pair of transverse slips, inserted near the ventral median line of 

 the serosa of the intestine and passing outwards dorsad of the great flexors to be attached 

 to the anterior edge of the fourth thoracic segment, pull the front of the intestine down- 

 wards and backwards. On each side, about halfway down the second abdominal segment, 

 two muscles diverge to the wall of the iutestine, the anterior being a retractor, the 

 posterior a protractor. A similar set are placed in the third segment ; acting together, 

 they would serve as dilators. 



Two muscles attached to the anal valve of each side are its apertors ; the one {lateral) 

 runs to the side wall of the fourth abdominal segment, the other {ventral) to its ventral 

 wall. 



Owing to the action of the muscles just described, the stomach and intestine move 

 backwards and forwards in a regular rhythmic sway. First the stomach moves upwards 

 and forwards, becoming strongly arched ; then backwards and downwards, flattening 

 again, so that the intestine forms at its commencement a vertical sigmoid loop ; third, 

 the rectum is pulled back, straightening the gut, and at this moment the anal valve 

 opens ; fourth, the anal valves close while the rectum is pulled forward, especially 

 at its hinder end. In this way it is obvious that the coelomic fluid is moved forwards 

 along the dorsal, and backwards along the ventral chambers left above and below the 

 alimentary canal *. 



The only accessory glands to the alimentary canal are the salivary [/lauds (PI. III. 

 fig. 6, sg.). In the fresh state, these form great paired botryoidal masses lying at the 

 outer sides of the labrum and epistoma. The cells do not show well in preserved 

 specimens, but in their place we find a pair of membranous nucleated sacs in the same 

 position, which bend in posteriorly and join on the middle line to a short chitinized tube, 

 which opens by a median salivary pore on the oral face of the labrum. 



I have attempted to show, in previous papers, that anal respiration is typical of 

 Crustacea. I did this in ignorance of the completeness of my case ; for Claus, whose 

 knowledge of the class is far above rivalry, ascribes, in his ' Crustaceen-System,' to his 

 " Protophyllopoda " (the supposed Crustacean ancestor) a short muscular rectum, sus- 

 pended to the body- wall and opening by dilator muscles into widely opening (" klqffen- 

 dem") lumen. In his ' Polyphemiden,' p. 10, however, published a year later, he expressly 

 denies, chiefly against Weismann, the respiratory significance of the process, as " regel- 

 massig und normal fur die Erhaltung des Organismus." After repeated observations of 



* Vernet describes a peculiar valve which I cannot identify, and ascribes a great part in this circulation to a 

 dilatation and contraction of the stomach, forgetting the physical impossibility of this process without the taking up 

 and discharge of liquid by the stomach, which does not occur, and which he does not assert. 



SECOND SERIES. — ZOOLOGY, VOL. V. ± 



