STRUCTURE OF EARTHWORM OP GENUS DIAOH^TA. 169 



the ventral vessel (fig. 12) the valve projected into the ventral 

 vessel^ thus showing the course of the blood to be from the 

 dorsal vessels through the hearts into the ventral vessel, as 

 in Lumbricus. 



§ Nervous System. 

 The position of the cerebral ganglia, as already mentioned, 

 is somewhat anomalous. They lie close to the posterior 

 boundary of a segment which, if the oviducts are to open on to 

 the xivth, and the other organs of the reproductive system to 

 be normally placed, must be regarded as the ivth, i.e. a seg- 

 ment further back than is usual. The cerebral ganglia give 

 off two intertwined bundles of fibres to the pharynx, which 

 represent the stomatogastric system, usually developed in 

 earthworms. There are not many data regarding the minute 

 structure of this stomatogastric system. In Megascolides 

 Spencer describes and figures (12) this system, and expressly 

 notes the absence of ganglionic corpuscles. In longitudinal 

 sections of Diachseta, the presence of numerous ganglion- 

 cells in the branches forming the stomatogastric system was 

 quite obvious. 



§ Testes, Sperm-sacs, and Vasa Deferentia. 

 In Diachseta Thomasii there are a pair of extraordinarily 

 long sperm-sacs attached in front to the septum separating 

 Segments xi, xii, and extending back through more than 

 twenty segments. Similar sperm-sacs have been described in 

 Urochajta (10), and, though much smaller, by myself in 

 Typhseus (4). I find, however, in DiachEeta two pairs of 

 these organs in the xith and xiith segments (fig. 9,vs), not at all 

 large, though containing abundant developing spermatozoa. It 

 is possible that the single pair of sacs described by Benham may 

 be the result of a fusion between two sacs on each side ; but 

 the matter requires further study, and, in the meantime, 

 Benham only discovered one pair of vas deferens funnels. 

 Two pairs of these organs were quite obvious in longitudinal 

 sections, and, corresponding to them, two pairs of testes in 



VOL. XXXI, PART II. NEW SER. M 



