5ââ ilENRY M. BERNARD, 



as acicular glands presents no greater difficulty than does the deve- 

 lopment of long ramified tubular tracheœ from the same starting 

 point. 



Continuing the row, we come to the spinning glands of the 

 Araneida. These are regarded, with almost general consent as de- 

 rivatives of setiparous glands, and would not here claim much attention 

 but for the light they throw on the tracheci\ It is difficult to avoid 

 the conclusion that they are homologous structures. The deduction 

 of tracheie from setiparous glands indeed necessitates this homology. 

 We should have no difficulty, then, in explaining why the spinning glands 

 arise in practically the same relation to the abdominal limbs as do 

 the tracheio. That some of the setiparous glands should form tracheiv 

 and some sericteries or spinning glands, is what we should expect 

 from what we have seen in the Hexapoda. 



It seems to me that there is nothing in the way of these homo- 

 logies except the Limulus theory of the origin of the Arachnids. 

 I have already pointed out some of the difficulties in the way of this 

 derivation, and here, surely, in these spinning glands on jointed leg- 

 like processes we find another serious difficulty. The spinning mamillae 

 are not easily deducible from the specialised abdominal plates of a 

 Limulus or a Eurypterid. The mamillse show no trace of having 

 passed through such a stage in their development, and, further, their 

 developmental history shows that they are not new structures but are 

 the rudiments of the abdominal limbs which the racial form of the 

 whole group possessed in almost every segment, and as such remind 

 us of nothing so much as the legs of Peripatus with their coxal 

 setiparous glands. 



In this connection I may mention that I have lately confirmed 

 the view of some earlier observers that the spinning gland of the mite 

 Tctranychus tiliarum opens at the tip of the pedipalp in a position 

 exactly corresponding with the spinning glands of Peripatus. This is 

 especially interesting because the mites show traces of being derived 

 from primitive Araneids. 



The Arachnids thus present us with a ventral row of structures 

 strikingly resembling the lateral row in the Hexapoda, both being 

 deducible from a row of acicular glands. Each contains salivary (or poison) 

 glands, spinning glands and trachea'. In the Arachnids, however, 

 a new development appears, viz : the coxal glands, which, I believe 

 with EisiG, may also be referred to setiparous glands. 



