The Genus Synchoeta. By 0. F. Housselet. 283 



whole eye-vesicle, and sometimes, congregating on either side of 

 it, give rise to an appearance of a double eye. From the eye two 

 narrow divergent tubules, as described in the introduction, advance 

 to the front of the head, and these tubules sometimes contain very 

 minute scattered red granules. I have counted ten and twelve of 

 these on each side on a recent occasion. 



The characteristic mastax is somewhat smaller in proportion 

 than in S. pectinata, whilst in structure it is very much like that 

 which is figured for S. ohlonga, pi. V. fig. 10. The unci are thin 

 triangular plates with five or six teeth, very irregular in shape 

 and divided in two sets by a deep incision (fig. 3b) ; the first tooth 

 is long and pointed and well separated from the rest, which is 

 characteristic of this type ; a very small knob of chitin at the back 

 of this first tooth indicates the spot where the manubrium is fixed. 

 The unci lie immediately below the mouth, and can readily be seen 

 from a frontal view in the living animal. I do not think the jaws 

 can be projected through the mouth as has been stated, and the 

 action of the mastax is the same as I have described in the case of 

 S. pectinata. The oesophagus is of moderate length and opens into 

 a saccate thick-walled stomach, the cells of which usually contain 

 yellow oil-globules. A small and densely ciliated intestine opens 

 on the dorsal side of the base of the body. The usual rounded, 

 or more or less pointed, gastric glands are readily seen. The ovary 

 is a fairly large and thick rounded plate on the ventral side, filled 

 with nucleated germ-cells. The lateral canals seem to be attached 

 to the wall of the stomach on each side, where they form some 

 convolutions, from which one branch runs forward and is attached 

 to the body-wall at a height corresponding to the middle of the 

 oesophagus, and there ending in two flame-cells on each side. 

 Two more flame-cells are seen lower down on the canal running 

 by the side of the stomach. No canal or flame-cell has ever been 

 seen in or near the head. The contractile vesicle is fairly large, in 

 its usual position above the foot. 



The longitudinal muscles, retractors of the head and foot, are 

 narrow and finely striated ; six to eight fine transverse muscular 

 threads run close together round the integument on the anterior 

 part of the body ; lower down there are fewer threads and they 

 seem to be confined to the dorsal side. 



The male, fig. 3a, was first discovered by Mr. Gosse ; it is a 

 small conical creature with a bent towards the ventral side close 

 behind the head. The front is truncate, with four styles. The red 

 eye, dorsal antenna, large sperm-sac, and two acute toes are pro- 

 minent. The mastax and stomach are quite absent, and replaced 

 by the sperm-sac. The size is 110 p, ( 2 £q in.) in length. I found 

 the male in some abundance in a gathering in October 1900, and 

 it is not very rare. 



Synchoeta tremula is a vigorous swimmer, and takes, as a rule, 



