388 SUMMARY OF CURRENT RESEARCHES RELATING TO 



close together. He regards the depression of the ectoderm during the 

 formation of the mesoderm as a rudimentary blastopore, and the cumulus 

 primitivus as its posterior margin 



The development of the external form is described in the second chapter of 

 the memoir, but hardly admits of brief summary. He points out inter alia 

 that Balfour has erroneously described the chelicerte in the embryo of 

 Agelena as in the form of pincers. The mandibular ganglion is not visible 

 from the exterior, and what Balfour figures as such is the basal joint of the 

 chelicerse. 



The organs derived from mesoderm and endoderm are in the third 

 chapter discussed at length. The somatic layer gives origin to (1) all the 

 musculature of the body except that of the mesenteron if such exist, (2) the 

 aponeurotic layer of the cephalothorax, (3) the sub-cutaneous connective 

 tissue and the lining membrane of all the organs arising by invagination 

 from the ectoderm, (4) the sarcolemma and neurilemma. The splanchnic 

 layer is the origin of the membrane of the midgut, the genital organs, the 

 pericardium, and the pulmonary veins. At the expense of the dorsal 

 mesenteron are developed (1) the heart, (2) the lateral arteries, and (3) 

 the mooring apparatus of the heart. The partitions give rise to the blood 

 corpuscles. The wall of the heart is formed by two mesodermic plates 

 which correspond to the dorsal mesenteron of Annelids. The cardiac wall 

 of Arthropods corresponds simply to the myocardium of Vertebrates. The 

 cavity of the heart corresponds to the segmentation cavity. The 

 pericardiac cavity in spiders, as in Mollusca and Vertebrata, is a part of the 

 coelomic cavity. 



The ectoderm gives rise to (1) the chitinous and chitinogenous layer of 

 the integument, (2) the epithelial layer and internal tunic of all the glands, 

 (3) the epithelium and internal lining of trachefe and lungs, (4) the 

 epithelium and lining of the oesophagus, rectum, stercoral pouch, 

 and Malpighian vessels, (5) the nervous system and eyes. The central 

 nervous system of spiders is derived from three ectodermic rudiments — (1) 

 two thickenings of the cephalic lobe, (2) two longitudinal thickenings of 

 the ventral wall of the embryo, and (3) a ventral median and unj)aired 

 rudiment. Its origin is exclusively ectodermic. The latter part of the 

 memoir is occupied with a general discussion of the homologies of the 

 nervous system of Bilateria, illustrated by diagrammatic figures. 



Reported Suicide of Scorpions.* — Prof. A. G. Bourne has made a num- 

 ber of experiments on three species of scorpions found at Madras, with the 

 object of determining whether or no scorpions are able to commit suicide. 

 He finds that it is undoubtedly physically possible for a scorpion to sting 

 itself in a vulnerable place, and when one is placed in very unpleasant 

 circumstances it not unfrequently lashes its tail about, and causes actual 

 penetration of the sting. But the poison of a scorpion is quite powerless 

 to kill the same individual or another of the same or even of another species ; 

 it is, however, very rapidly fatal to a Thelyphonus, less rapidly so to a spider, 

 and much less rapidly so to an insect. Two scorpions, when fighting, 

 repeatedly sting one another with little if any effect, the stronger killing 

 the weaker by actually pulling it to pieces with its chelicera3. Scori)ions 

 cannot stand even a dry temperature much above 50° C, but fall into a sort 

 of " heat coma," and soon die if the temperature be raised. The poison 

 may be pressed out of the sting with the fingers or a pair of forceps, when 

 it is found to be a milky white fluid with a very pungent smell, resembling 

 that of formic acid. 



* Proc. lioy. Soc, xlii. (1887) pp. 17-22. 



