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tions. The claws of the true legs are pretty well developed. The 

 contractions of the dorsal vessel are less violent than yesterday ; have 

 increased to 55 per minute ; and can be traced through half the length 

 of the embryo. I could not, under any circumstances, detect any 

 movement of a circulating fluid. Bristles begin to appear on the 

 feet, and the pro-legs are developed. The tracheary system is faintly 

 marked out in the vicinity of the head, though the coiled spring could 

 barely be discerned in one of the largest trunks. A mysterious vital- 

 ity inheres in this forming organism, as the following experiment shows. 

 The egg was put under the compressor, and pressed till the outer mem- 

 brane burst, and the tail of the embryo was extruded : in this condi- 

 tion, the contractions of the dorsal vessel increased to 80 per minute. 

 On further compression, the contractions near the head were 68, 

 and near the tail 144, per minute. On still further compression, the 

 contractions near the head remained the same ; while those near the 

 tail occurred by threes, in which the beats were very quick. The 

 compression was increased as far as the thin glass could allow : the 

 embryo Avas completely crushed, and its parts extruded in every direc- 

 tion ; and yet, where the dorsal vessel lay, the wondei^ful struggle to 

 perpetuate existence was kept up to the end. 



June 14. The ova are beginning to hatch. The slug cuts a semi- 

 circular slit through the membrane of the egg and the epidermis of the 

 leaf, forming a lid,^ which folds back, and allows it to escape. One slug, 

 which had not moved its own length from the trap-door through 

 which it emerged, was .06 of an inch in length. In form, the young 

 slug slightly increases in width from the tail to the region of the head, 

 where it exhibits a considerable enlargement. The head is black, and 

 habitually curled under the shoulders : it is furnished with a powerful 

 pair of serrated mandibles. The eyes can be seen, under pressure, as a 

 pair of small round, clear globules ; in front of which is a pair of oval 

 semitranslucent spots. The feet are provided each with a bifid claw 

 and several short bristles. The pro-legs are truncate, smooth, and 

 retractile : a few bristles are seen scattered in clusters of two and 

 three over the exterior, and they become more numerous at the poste- 

 rior extremity. The external surface is transversely wrinkled, and 

 covered with a small amount of watery slime. The young slug is 

 nearly transparent, but having a pale, olivaceous hue, with a dark 

 spot at one extremity produced by the head, and another at the oppo- 

 site extremity caused by an accumulation of fecal mattei-. 



The alimentary canal in the new-born larva is by far the largest 

 vessel in the animal. It swells out to its largest diameter just behind 

 the head, and somewhat irregularly tapers toward the hind extremity, 

 near which it is much contracted. In this part of the slug, numerous 

 faint, parallel, longitudinallines can be seen, which are perhaps muscu- 



