334 Thos. H. Montgomery. 



Claparede (1862) saw no segmented stage earlier than that of six 

 cephalothoraeic segments, and described these as appearing simul- 

 taneously; the rostrum comes from an unpaired anlage. Balbiani 

 (1873) found the earliest segments to be the pedipalj)al and the 

 segments of the first two leg pairs (these nearly synchronously), 

 followed by those of the third and fourth legs, then by the most ante- 

 rior (cheliceral) which arises from the cephalic lobe. Balfour 

 (1880) described a stage with procephalic and caudal lobes ''and 

 about three segments between the two," which segments, he considered, 

 are probably those of the first three leg pairs; the pedipalpal and 

 cheliceral segments are later in origin, and the cheliceral cuts off 

 from the head lobe. The mesoblast of the head lobe (procephalic 

 lobe) is separated from that of the chelicera, and the two coelomio 

 sacs that compose it are connected in the midline around the stomo- 

 daeum. "The procephalic lobe represents the preoral lobe of Chaeto- 

 pod larvae." The chelicera are postoral in position, arising behind 

 the ectoblastic stomodaeum, "and terminate in what appear like 

 rudimentary chelae" — an observation shown by Schimkewitsch to bo 

 erroneous. Croneberg (1880) found that the rostrum is formed from 

 a paired anlage, and equals at least one pair of extremities. Locy 

 (1886) observed the earliest segmental stage to consist of "three 

 zonites and the cephalic plate. * * '" The addition of new 

 zonites to those already existing goes on rapidly; the two anterior 

 ones (those of the chelicerae and the pedipalpi) are cut off from the 

 posterior end of the cephalic plate. * * * The other zonites 

 are developed from the caudal plate." * * * ^ "prominent 

 upper lip composed of two lateral elements" later arises just anterior 

 to the stomodaeum. The ventral sulcus is produced by the mesoblast 

 separating medio-ventrally. Lendl (1886) alone claimed to observe 

 a segment arising between the cheliceral and the pedipalpal ; this 

 "mandibular" segment is said to develop a pair of "mandibles" that 

 later fuse with the unpaired rostrum. Morin (1887) described the 

 germ disc as becoming triangular, the broader end of which (Vorder- 

 lappen) represents the anlage of the cephalothorax ; the first segment 

 to appear in the sixth, then the fifth, and so on from behind for- 

 ward, the cheliceral last; there is an independent pair of coelomic 



