21 8 DESCRIPTIONS OF PREPARATIONS. 



Aulostoma. Haycraft (P. R. S. xxxvi. 1883-84, p. 478) has proved that the 

 secretion of the pharyngeal glands has the power of arresting coagulation in blood 

 apparently by destroying the coagulation ferment. The muscle cells of the ' crop ' 

 are for the most part disposed in a transverse direction, and their ends are branched. 

 Its epithelium is low, columnar, and the cells, according to Gibbs Bourne, may be 

 seen giving off clear droplets into the blood. In Aulostoma the alimentary epi- 

 thelium is ciliated. Its food consists of worms, &c. Moquin-Tandon states that 

 when young this Leech possesses distinct lateral caeca to the crop in addition to 

 the posterior pair. The region of the crop is not sacculated in Nephelis, Trocheta, 

 or Pontobdella. In the last two it is constricted at intervals, and the last-named 

 possesses a posterior azygos caecum underlying the stomach. Trocheta is carni- 

 vorous like Aulostoma. 



The body-cavity or coelome is in all adult Leeches almost obliterated by 

 connective tissue growths. This process of obliteration of the coelome is termed 

 by Gibbs Bourne diacoelosis. The remains of the coelome are much more 

 conspicuous in the Rhyncho- than in the Gnathobdellidae. In the medicinal Leech 

 its chief remains are in the form of the dorsal and ventral sinus, the latter lodging 

 the nerve-cord. They are in direct connection only by means of the dorsal sinus 

 of the gastro-ileal section of the alimentary canal. Other remains of the coelome 

 are found in the network of vessels surrounding the testes, &c. The blood-vessels, 

 which with their branches have muscular walls, are represented by a right and left 

 longitudinal trunk which anastomose at the anterior and posterior extremities of the 

 body. These trunks give off in each somite later o-abdominal vessels which anas- 

 tomose ventrally, and two sets of dorsal vessels, short latero-lateral and long 

 latero-dorsal branches. In the gastro-ileal region the latter anastomose inter se 

 dorsally by means of their posterior branches. Anteriorly to this region they are 

 connected only through the capillary system of thin-walled vessels. There is a 

 superficial network of fine capillaries which penetrate the hypodermis, and more 

 deeply pass into an intermediate layer connected with the lateral vessels and with 

 the botryoidal tissue. The latter forms the deepest layer, connected on the one 

 hand with the vessels given off from the lateral vessels, on the other hand with the 

 sinuses. It tends to form a secondary coelome (= metacoelosis, Gibbs Bourne). 

 The dorsal and ventral sinuses, according to Gibbs Bourne, communicate with (i) 

 the cutaneous network, (2) the capillaries of the crop, and (3) of the stomach, and 

 (4) the sinuses (moniliform hearts of Brandt) which surround the nephridial funnels 

 and lie upon the testes. 



The thin-walled capillaries of the Leech possess no endothelium and no nuclei. 

 The walls of the vessels in the botryoidal tissue are formed solely by the pigmented 

 cells themselves. The blood-plasma in the Gnathobdellidae, but not in Rhyncho- 

 bdellidae, is coloured red by haemoglobin. It contains amoeboid corpuscles, and 

 here and there Prof. Ray Lankester detected nuclei set free from the walls of the 

 developing capillaries, as in the Earthworm. But they appear to be very scanty in 

 number in the Leech. 



Bite of Leech, Carlet, C. R. 96, 1883. Lime in teeth, Schneider Zool. Beitrage, 

 i. 1885. 



Alimentary canal. Gratiolet, A. Sc. N. (4), xvii. 1862, p. 182; Gibbs Bourne, 

 op. cit. p. 492. 



