MOUNT ST. GOTHARD TUNNEL LABOURERS. 143 



with chitinous (?) teeth, bounding a triangular space in the central 

 portion. The pharyngeal canal has very strong and muscular par- 

 titions. It is continued in the intestine of a cellular nature, with 

 its internal cavity disposed in zigzags, more or less wide, and termi- 

 nates in the arms situated upon a small external lateral projection. 

 Towards the middle, on the oral side of the larva is already to be 

 seen a small ovoidal body which pushes inward the intestine and is 

 found on the external part, niched in a corresponding depression of 

 the muscular-dermical layer of the larva. This small body is the 

 rudiment of the genital apparatus which appears very conspicuously 

 .in the embryo, and is observed more or less distinctly in the diffe- 

 rent periods of development of the larva towards the free state. 

 When one day old, the larvae are already 250/z. long, and, in the 

 mean, I have calculated that, if the temperature does not exceed 24 

 to 25 deg. centigrade, with temporary diminutions, they attain about 

 50^. each day. At a higher temperature and under more favourable 

 conditions, they may even attain from 80 to 100^. in length, and 

 2/jL. in transversal breadth per day. Their greatest length, how- 

 ever, is about 550;Lt. and breadth from 20 to 24^. 



After eight hours' life of the larvae, I have seen the waving zig- 

 zag disposition of their intestinal canal disappear with increase of 

 growth, the intestines become straight and indicate the longitudinal 

 axis of the body. The larvse, at first weak and moving only in the 

 temperatures adapted to them, become robust, and in a few days 

 have a snake-like motion, even at a temperature of 14 to 16 deg. cent. 

 They undergo no change ; but when they have reached the maxi- 

 mum length and breadth, a great change manifests itself in their 

 pharyngeal canal. It may be said that this canal melts, to be trans- 

 formed gradually (in a day and a half to two days) into another 

 pharyngeal canal differing in its structure to that met with in the 

 new-born larvae before the incapsulation. Whilst the pharynx is 

 greatly modified, the skin separates a substance chitinoid (?) glassy, 

 transparent, which in a very short time is condensed, and forms a 

 capsule which encloses the living larva. This is seen to move freely 

 in its capsule or cyst, which completely repeats its shape. The in- 

 capsulation having taken place, the mouth changes, presenting 

 already the rudiments of the hooks and stings ; the new pharyngeal 

 canal is perfected, whilst the intestine loses its primitive structure, 

 the number of granules diminishes, becomes more transparent, with 

 very fine granules and particular disposition of the elements. Be- 



JouHN. Q. M. C, No. 44. m 



