ZOOLOGICAL POSITION OP LIMULUS. 221 



PI. XXXIII, do not reach so near the edge of the carapace and cease to affect it by the 

 appearance of sutures on the surface. The edge of the head-shield is fringed with hairs. 

 The edge of each segment of the thoracico-abdominal somites is toothed, the basal 

 tooth being the largest, the succeeding ones more minute, and with a movable spine 

 inserted on the posterior border of each serration and projecting beyond it (see figs. 10, 

 11 and 12, t, a, PL XXXIII). The border of these somites is also fringed with 

 minute hairs. 



Appearance of young Limulus after the first moult. 



The first moult observed by Dr. Packard occurred about the 25th of July, three 

 weeks after hatching. The principal changes are the possession of a short abdominal 

 spine, the origin of a fourth pair of thoracic branchigerous lamellae, and the appearance 

 of additional joints to the opercular plates, and the smaller and more numerous lobes of 

 the liver. 



Regarding the age of sexual maturity, and the period when the external male 

 characters appear, Dr. Lockwood thinks that the time of puberty cannot come before the 

 third or fourth year, and considers that the latter figure may prove the minimum. It is 

 not until this period is reached that " the male undergoes its last metamorphosis." It 

 then nioults, and the antennal claws assume the peculiar shape of that sex 1 (see PI. IX, 

 fig. 1 a). 



The Zoological position of Limulus considered. 



Having briefly described the larval stages of Limulus I will pass at once to 

 the conclusions arrived at as to the position of Limulus with regard to the other 

 Crustacea. 



Whether Limulus does or does not descend from a Nauplius, Dr. Dohrn considers 

 that at present we have no knowledge of a Nauplius-stage in that genus, any more than 

 in the Trilobita; but the subsequent stages agree with such forms as Trinucleus and Sao, 

 in the gradual development of the young from a form having a simple cephalic and 

 caudal plate to the adult stage in which numerous intermediate body-rings have been 

 added. Dr. Dohrn further concludes that Limulus cannot be retained among the 

 Crustacea, for two reasons. 1st. Because of the presence of only one pair of extremities 

 which are supplied with nerves from the suprabesophageal ganglion. 2 2ndly. From the 

 position and form of the under lip. 



1 When adult, the males in Limulus moluccanus have the chelae of both the 2nd and 3rd pair of 

 appendages modified, so as to form powerful recurved monodactylous claws, which shut against a projec- 

 tion from the penultimate joint. (Vander Hoeven, op. cit., pi. i, fig. 3.) 



2 This was first asserted by "Vander Hoeven in his 'Recherches sur l'Histoire Naturelle et 

 l'Anatomie des Limules,' 1838. 



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