974 SUMMARY OF CURRENT RESEARCHES RELATING TO 



that the nucleus is apparently all that is present, and hence they are 

 called "ganglionic nuclei " by Dietl. These latter occur only in the 

 brain, and more especially in the optic portions of it. They resemble 

 similar cells in insects. The ventral chain consists, as has been 

 shown by Schimkewitsch, of live thoracic and one abdominal ganglia, 

 fused across the mid-line. 



The author describes the arrangement of ventral ganglia in 

 Scorpio. Here, the last lobe of the ventral ganglionic mass, repre- 

 senting the ganglion for the pectines, has a structure similar to that 

 of the antennary ganglion, and tin's lends support to the opinion that 

 the firmer are sense-organs. Nothing like it is found in the Araneina 

 nor in the Phalangida. 



Arterial System of Scorpions.* — M. F. Houssay describes the 

 arterial system of scorpions as being formed of two groups of vessels, 

 dorsal and ventral, which are connected with one another by two 

 short vessels at the anterior end, and by an unpaired canal in the 

 middle of the body. The anterior aorta gives off four arteries, and 

 itself terminates abruptly and without ramifying in the cerebroid 

 ganglia. The ventral group is interesting on account of its re- 

 lations to the nervous system ; the blood occupies the space between 

 the two nerve cords which connect the ganglia ; from the cephalo- 

 thoracic perineural lacuna five trunks are given off on either side. 



The connecting arteries of the anterior end envelope the con- 

 nectives which go from the cerebroid ganglia to the ventral mass. 

 They afford a means of communication between the perineural lacuna 

 and the anterior aorta. The median limb of connection arises from 

 the posterior aorta in the middle of the seventh ring of the " pro- 

 abdomen," and opens into the perineural canal. The author points 

 out the resemblance between this arrangement of the vessels of 

 scorpions and that which obtains in Limulus and the Myriopods. 



Embryology of Spiders. f — Dr. A. T. Bruce writes that some 

 work done during the past winter on the embryology of several 

 species of spiders, at the biological laboratory of the Johns Hopkins 

 University, brought to light some facts of general interest. 



The origin of the lung-book of the spider is particularly interest- 

 in ', in view of the comparisons instituted between Limulus and the 

 Arachnids. From good longitudinal sections of the spider embryo 

 before the disappearance of the abdominal feet, it apj)ears that the 

 lung-book may fairly be regarded as an involuted appendage or 

 appendages. Before the involution of the abdominal appendages, 

 the epithelium covering them assumes the characters of the epithelium 

 of the lung-book. At the same time the appendages become less 

 conspicuous, and slight folds appear on their anterior faces. 



By the complete involution of the abdominal appendages, and 

 the increase in the number and distinctness of the folds on their 

 anterior faces, a lung-book would be formed with its laminae directed 

 backwards. All the stages of the process of involution were not 



* Comptes Eendus, ciii. (1SS6) pp. 354-5. 

 t Amer. Natural., xx. (1886) p. 825. 



