ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 993 



that the muscles of the appendages of the mesosoma, which are large 

 in Limulus, would be almost or altogether suppressed in Scorpio. The 

 most remarkable agreements are to be found in the large number of 

 muscles attached to the prosomatic entDchoudrite, in certain of tV.e 

 muscles attached to the pectines in Scorpio and the first gill-bearing 

 appendages of Limulus, and in the muscles arising from the peri- 

 cardium and inserted into the investment of the great venous sac, 

 which in tlie one case lies at the base of a gill-book, and in the other 

 case forms the investment of the in-sunken lung-book. 



In a comparison of these two forms it is to be recollected that in 

 both cases we have to do with highly specialized conditions; the 

 common features of the less modified ancestor are sketched, and the 

 lines of development pointed out ; some of the muscles must be 

 looked upon as new developments in Limulus, where they appear to 

 be more largely represented than in Scorpio ; in the former there has 

 been a peculiar consolidation of the merosomatic region and the com- 

 bination of natatory with branchial functions in its appendages ; in 

 the scorpion development and modification are most apparent in the 

 limbs of the prosoma. 



In conclusion, Prof. Lankester has some observations on those 

 characters of the group which are useful in classification ; here 

 account must be taken not only of Peter's characters — form of the 

 sternum and dentition of the chelicerfe — but also of the disposition 

 of the segmental ganglia with their great nerves, and the sculpturing 

 of the lamellse of the lung-books. The class Arachnida is regarded 

 as consisting of two grades : A. Delobranchia (Limulus and Euryp- 

 terines), and B. Einholobranchia (Orders 1. Scorpionidea ; 2. Pedi- 

 palpi ; 3. Araneidea). The Scorpionidea consist (jf a single family, 

 divisible into the Scorpionini and Androctonini. Fifteen points are 

 mentioned which are regarded as of importance in the systematic 

 descriptions of these arthropods. 



Sense-organ of Spiders. — Prof. W. Schimkewitsch describes* 

 briefly a sense-organ on the limbs of certain spiders, which was first 

 noticed by Dahl. These structures are found on most of the joints of 

 the limbs both in males and females ; they consist of a thin chitinous 

 plate with a thick border, the opposite sides of which arc connected 

 by parallel thickenings. A transverse section shows round these 

 organs a layer of remarkably tall pigmented cells, between these are 

 ganglion cells with prolongations directed towards the chitinous layer. 

 These organs appear to be comparable to the " chordotonal organs " of 

 insects described by Graber. 



Dr. P. Bertkau claims priority f in the discovery of the sensory 

 organs on the limbs of sjjidors referred to by Schimkewitsch. A brief 

 recapitulation of his results is given. 



Seasonal Dimorphism in Spiders. — Dr. P. Bertkau states f that it 

 is not a now discovery of Dahl's that Meta segmentata and M. mengei 

 are two broods of the same species, § but it has been known and recorded 



• Zool. Anzeig., viii. (1885) pp. 264-0. t Ibid., pp. ."i.ST-S. 



♦ IJ.i.l., pp. 4.VJ-64. § S<f tlii.s Jr)iiiiial, 'intc, p. S.^O. 



