394 



Prof. E. R. Lankester. 



[June 16, 



anterior appendages, which has, in the case of the whole group of 

 Eurypterina, led to the suppression of the foremost pair of appendages 

 corresponding to the cheliceree of the Scorpion and of Limulus. The 

 probability of such a suppression having taken place has a direct 

 bearing upon questions which arise when a comparison is attempted 

 between the series of appendages of the Arachnida as a class with 

 those of other classes of Arthropoda. It is significant in this con- 

 nexion that such a suppression of at least one pair of anterior 

 appendages has been very generally considered to be a characteristic 

 of the Arachnida, whether the attempt to harmonise their structure 

 with that of other Arthropoda has been made in assimilating them 

 through Galeodes to the Hexapod Insects, or through Scorpio to the 

 Decapod Crustaceans. 



I now submit as a summary of the conclusions to which I am led, a 

 tabular view of the structural identities of Limulus and Scorpio, in 

 so far as the sclerites of the body and appendages are concerned ; and 

 shall next describe certain cavities and their stigmata which I have 

 detected in Limulus which appear to me to be the representatives of 

 the stigmata of the pulmonate Arachnida, and of the pulmonary 

 chambers in which their gill-books have become concealed.* 



Notes in reference to the Tabular Statement. 



Gamer ostome. — The tubercular sclerite at the base of the first pair 

 of appendages overhanging the mouth may be spoken of by this term 

 (introduced by Latreille) both in Limulus and the other Arachnida, 

 without prejudging the question as to its relations to the "labrum" 

 of Hexapod Insects or of Crustacea. 



Ghilaria. — This term has been applied by Professor Owen to the 

 pair of small processes placed mesially between the coxa? of the last 

 pair of legs in Limulus. Although supplied by distinct nerves, yet 

 their late appearance in development, as shown by Packard, and their 

 simple structure, lead to the conclusion that they are not rudimentary 

 appendages, as has been supposed, nor parts of the coxge of the sixth 

 pair of legs as has been suggested, but special tubercular elevations 

 of the sternal surface. 



Genital operculum, — On account of the concentration of the nerve- 

 centres in the cephalo-thoracic region, and the consequent origin of 

 the pair of nerves to this organ from that region, the genital oper- 

 culum Limulus of has been regarded by some writers as belonging to 



* [June 24th, 1881. In October, 1878 ("Quart. Journ. Micr. Science") I 

 published an account of the motility of the spermatozooids of Limulus. This 

 character tends to separate Limulus from Crustacea. It also tends to unite Scorpio 

 and Limulus. The most important difference between the two animals, is the 

 absence from Limulus of Malpighian tubes. Rudiments of these may yet be dis- 

 covered.] 



