486 Mil. J. GRAHAM KERU O]^ [Nov. 19, 



backward prolongation of the testis figures in the current de- 

 scriptions of Protoj)terus as the vas deferens ; while for Lejpidosiren 

 Ehlers has denied the existence of any opening to the exterior at 

 its hind end. 1 will describe it as the vesicular region of the 

 testis ' (text-fig. 49, T, p. 145). 



The vesicular portions of the two testes run backwards, gradually 

 converging towards a point in the region of the genito-urinary 

 openings. These openings, which become during the breeding- 

 season marked each by a prominent papilla, are situated on the 

 dorsal wall of the cloacal caecum just within its opening into the 

 cloaca. The cloacal caecum of Lepidosiren and Protoj^terus, whose 

 morphological nature has hitherto been uncertain, I may mention 

 parenthetically, arises in ontogeny in the following way : — In stage 

 85 ~ the kidney-ducts open separately into the cloaca just within 

 its external opening, one on each side. In stage 36 the two ducts 

 have united distally, and their united portion is beginning to 

 project slightly forwards. Later still the fused portion becomes 

 much dilated and its projection forwards forms a large pocket — 

 the caecum. The caecum is then to be looked on as a projection 

 forwards of the uriiio-genital sinus, and is probably morphologically 

 comparable with the sperm-sacs of the Selachian — the forward 

 projection in this latter case being deeply bifid— and with the 

 urinary bladder of Ganoids and Teleosts. 



On examining transverse sections, the sperm-producing region 

 of the testis is seen to be composed of numerous rounded ampullae 

 disposed in a somewhat radial fashion in a stroma of dense connec- 

 tive tissue. The ampullae open into a longitudinal canal which 

 posteriorly approaches the dorso-median surface of the testis, and 

 is continued back as the cavity of what I have termed the vesicular 

 portion of the testis. In this region the functional seminiferous 

 ampullae disappear, though there may be present one or more little 

 aggregations of these, as mentioned by Ehlers, behind the main 

 body of the testis. 



Thi'oughout about the first quarter of its extent the vesicular 

 region of the testis is a simple tube with fairly smooth outer surface, 

 its cavity lined by cubical epithelium, and broken in upon by tra- 

 beculae passing inwards from the wall. Traced backwards, however, 

 the wall of the tube becomes irregular, longitudinal ridges and other 

 projections appear which sometimes leave the surface of the testis 

 and run backwards in bridge-like fashion to rejoin it later on 

 (c/. Plate XXVII. fig. 1, T^). The lumen of the tube becomes 

 correspondingly broken up, and the dorsal portion of this region 

 of the testis assumes the character of an irregular sponge-work 

 with hollow trabeculae, which contain prolongations of the central 

 lumen. In its most posterior portion the testis is closely applied 

 to the ventral edge of the kidney, and the trabeculae of the testicular 



^ Ehlers also emphasizes this division of the testis into two regions {op. 

 cit. p. 12). 



^ /. e. the stage represented by figure 35 of my paper " On the External 

 features in the Development of Lcpidosiren," Phil. Trans, vol. 192B. p. 299. 



