NOTES AND MEMORANDA. 



423 



wliicli a number of interlaced bands and elongated connective-tissue 

 nuclei can be made out. The name perineurium is applied to the 

 general investment of the nervous system, while that of neurilemma is 

 applied only to the coverings of the separate nerve-fibres. The tissue 

 ordinarily known as the outer neurilemma is stated to belong to the 

 connective tissue of the body cavity. As to the nervous elements, he 

 agrees generally with Dietl, but he finds a number of nucleoli in the 

 nuclei of the large ganglion-cells, and also notes that the " tubular " 

 nerve-fibres do not appear to be formed of primitive fibrillee, but to be 

 composed of a strong sheath containing a clear viscid fluid. 



The dotted substance of Leydig is found to be composed of a 

 number of distinct spheres, which are arranged in pairs, which, again, 

 are ordinarily connected by a transverse commissure, or a bridge of 

 dotted substance. Each sphere gives ofi" a peripheral nerve, or a com- 

 ponent part of one. Of these spheres there are eight in the cerebrum. 

 The anterior give oft' fibres for the optic nerves : of those that succeed 

 them, the outermost provide for the outer antennse, and the others for 

 the inner antennte and oj)tic chiasma respectively. In the sub- 

 oesophageal ganglion there are seven pairs, five of which are connected 

 by a bridge and commissure, and two by a bridge only. Each of the 

 thoracic ganglia is provided with a pair ; in the abdominal ganglia 

 there are two pairs, one ellipse-shaped and one spheroidal ; the caudal 

 (post-abdominal) ganglia are foimd to have five pairs. The greater 

 part of what follows is only intelligible to those who have Dietl's 

 figures at hand, but it may be noted that the nerves arising from the 

 ganglia are stated to be generally made up of two parts, and that the 

 so-called giant nerve-fibres pass through the whole of the ventral cord. 



Heart of the Crayfish, and Lobster. — The following results are 

 given by Deszso * on this subject : — (1) There are five pairs of clefts 

 on the dorsal surface, of which four are so small as to require 

 careful search. On the ventral sui'face there are three pairs, two of 

 which are very small. (2) The musculature of the organ is composed 

 of muscle-cells, and not, as has been supposed by Weissmanu and 

 others, of mere muscle-fibres ; these cells have the transversely striated 

 substance on one surface only. The nuclei of the muscle-cells are 

 provided with nucleoli, which may often be observed in the act of 

 fission. In the lobster the anatomical elements are much smaller 

 than in the crayfish. In the muscular wall of the heart there are 

 eight haemal spaces corresponding to the eight clefts, and these spaces 

 unite in a central ventricle. (3) The pericardium is an elastic layer 

 of connective tissue, in which a few small nuclei can be made out ; it 

 is not provided with any muscular elements. (4) In the posterior 

 region of the dorsal part of the muscular heart, ganglionic cells, ordi- 

 narily bipolar, and invested in connective tissue, may be discovered. 

 These are often united together by threes, or in a larger number ; the 

 largest of them were found to measure ^^ of a millimetre, their nuclei 

 t3q%, and their nucleoli -jis of a millimetre. 



The same author gives f a very brief account of the connection 



* ' Zool. Anzeiger,' i. (1878) 126. t Ibid., 274. 



