432 TRANSACTIONS OP SECTION D* 



of the lateral margins this articulation is about a quarter of the length of the 

 hypostome from the front. The hypostome has further a prominent central pro- 

 jection. The whole length of the hypostome is about half that of the carapace. 

 The front margin of the carapace turns down and then turns in on itself, 

 This turned-in portion is articulated to the turned-down part so as to be capable 

 of free movement, and the turned-down part is marked by a suture which was 

 probably also capable of movement. The size and formation of the hypostome 

 render it extremely improbable that the mouth opened behind it. Apparently 

 the arrangement was that the hypostome, turning on its articulation, projected 

 its anterior margin ventrally, while the inturned margin of the carapace also 

 projected ventrally, the two forming lower and upper lips respectively to the 

 mouth. 



In a line between the lateral margin of the glabella and the eyes there has 

 appeared a long conical structure divided into joints by strong annular thicken- 

 ings and also furnished with finer annulations. This structure is more than two- 

 thirds the length of the carapace and has a breadth at its posterior end of one- 

 eighth of its length. I have been unable to find it on the other side of the 

 specimen, but the specimen was cut just along that line by a lapidary's wheel, 

 which may have destroyed it. The posterior end lies in the horizon of the 

 second free segment, but as the ventral membranous body-wall is not distinct, it 

 is impossible to say whether it is precisely in situ or not. The structure cer- 

 tainly resembles an antenna more than anything else and must have been joined 

 to the body-wall behind the hypostome, as otherwise it could not have been 

 withdrawn when the animal rolled itself up. The antennae described by Beecher 

 in Triarthrus also arise pretty far back. This has given rise to some confusion, 

 owing to the popular idea that an antenna must arise from the head. Morpho- 

 logically that is true, but post-oral appendages may assume an antennary function 

 and structure, as in Phrynus and Thelyphonus, and we probably have such a 

 case in these Trilobites. Any discus'sion of the probable morphological bearing 

 of the two points I have described here is better postponed till our knowledge 

 is a little further advanced. 



I hope to communicate a fuller account of these and other points to the 

 Royal Society of Edinburgh during the coming session. 



3. The Crop of the Leech. 

 By Professor Marcus Hartog, M.A., D.Sc. 



As seen but never fully studied by the older observers, but apparently for- 

 gotten latterly, the crop of the leech is divided into eleven chambers ; these are 

 separated by distinct simple septa passing inwards from the obvious external 

 constrictions, and perforated by a central hole, circular under ordinary condi- 

 tions, but vertically elongated in distension, having the form of an inverted 

 isosceles triangle with rounded angles. The septum shows a beautiful puckering 

 at the free edge and capillaries loop over it, and contains a circular sphincter, 

 but no divaricator fibres; it is bounded laterally by the posterior dorsiventral 

 muscles, which run in the constrictions. Similarly the anterior dorsiventral 

 muscles run in the less marked constrictions across the middle of each chamber. 

 Successive truncheons of the hardened distended leech are necessary to display 

 the structure, which is inconspicuous in ordinary dissection, and which is not 

 easily recognisable in the usual transverse thin section. 



4. Lantern Demonstration illustrating the Development of the Starfish Solaster 

 endeca (Forbes). By James F. Gemmill, M.A., M.D., D.Sc. 



Egg yolky ; segmentation total, equal ; blastula formation much as in Crib- 

 rella; gastrula by invagination; a free swimming 'larval' stage without mouth, 

 and with blastopore closed ; larva with three arms and a sucker ; metamorphosis 

 occurring in such a way that, while in point of external form the left side of the 

 larva becomes the oral surface of the starfish, in reality the epiderm of the oral 

 surface is partly derived from that of the preoral lobe. The aboral surface of 



