422 Dr. A. Strubell on the 



pronounced convexity, which does not become incavatcd until 

 later. 



The changes which now take place and are externally 

 visible are primarily exhibited in the further development of 

 the segments of the body which have already been mentioned. 

 In the first place the abdomen again increases considerably 

 in size. While more segments are continually separated off 

 from the median unpaired abdominal plate, the latter with 

 its adjoining abdominal divisions moves out from its previous 

 horizontal position, and gradually projects forwards at an 

 acute angle. 



The formation of the twelfth pair of abdominal segments 

 completes the series ; the abdominal plate then lies as a 

 terminal piece at the tip of the abdomen, and from it the 

 caudal filament is subsequently developed. It is especially 

 worthy of remark that provisional appendages, such as those 

 with which we are acquainted in the case of the scorpions 

 and the true spiders, are not to be found at any period upon 

 the abdominal segments of Thelyphonus. On the other hand, 

 small thickenings appear at an early period on the inner 

 margin of the several segments, and, gradually becoming 

 more sharply defined, represent the ganglia of the abdominal 

 portion of the ventral chain. 



If we now take a lateral view of the ovum, we observe 

 that the upper portion of the ventral surface has become 

 flatter, while the posterior division projects somewhat towards 

 the protruding abdomen. The development of the embryo 

 now makes rapid progress. Two semicircular pits appear at 

 the hinder margins of the apical lobes. The labrum becomes 

 visible above the mouth, while the labium arises as a narrow 

 protuberance at its lower border. In proportion as the brain 

 continues to develop the further forward does the mouth 

 advance, until it finally comes to lie between the chelicerse, 

 which are situated close to one another. The limbs, too, have 

 in the meantime increased in length and their segmentation 

 is already visible, although not yet distinct. 



Simultaneously with this a peculiar hemispherical structure 

 comes into view between the first and second ambulatory 

 limb. It first appears as a small lateral prominence at the 

 base of the second limb, which is still knob-shaped ; but it 

 soon becomes constricted off, and then assumes the above- 

 mentioned position. I am unable to make a definite state- 

 ment as to the significance of this organ. The fact that at a 

 spot on the inner side of the chorion corresponding with this 

 body a brownish substance is excreted, which projects like a 

 tooth between the two limbs, seems to betoken a secretory 



