On the Life-Hìstory and Development of the Genus Myzostoma. 549 



veiy widely apart. They are not veiy numerous, and in the wbole series 

 of sections of oue animai not more than seven or eiglit were found. The 

 only case in which I found them was in a perfectly normal individuai 

 31. glabrum, killed with osmic acid. I have never found them before 

 or since. Their only possible function must be that of touch. 



It is very curious that they should only have been found in one in- 

 dividuai, and this fact I can only explain by the supposition that they 

 are disappearing sense organs. In the particular individuai in which 

 they were found their presence may be due to a reversion to an ancest- 

 ral condition. Their absence in other individuals cannot be explained 

 as due to bad preparation , for they were not to be found in specimens 

 prepared in exactly the same manner as this particular individuai, and 

 indeed prepared with special reference to these supposed sense organs. 



Nervous System. 



The nervous system was first discovered by Lovén, and was des- 

 cribed more in detail by Semper i in M. glabrum. Semper referring to 

 its fìner structure says: »Es besteht nämlich aus einer feinkörnigen 

 äußeren ziemlich dicken Schicht, und einer centralen länglichen Masse, 

 welche innen ziemlich viel dunkler gefärbt ist , als die Rindenschicht 

 und aus zelligen Elementen zusammengesetzt zu sein scheint. . . . An 

 frischen, in Seewasser untersuchten Präparaten sieht man jedoch deut- 

 lich, dass diese centrale Masse ganz abgeschlossen ist und auf keine 

 Weise durch Fasern mit den Nerven in Verbindung steht.« The central 

 mass described by Semper was considered by Graff2 to be made up of 

 large ganglionic cells. 



With regard to the finer structure of the nervous system, it is in- 

 deed divisible into a central dark mass and an outer lateral much 

 lighter portion. The lateral mass however is not »feinkörnig«, but rather 

 composed of numerous nerve fibres and connective tissue Clements 

 (figs. 33 and 34). It contains but few cells, and these apparently all 

 or mostly connective tissue cells. As one might expect the central mass 

 is not closed off from the lateral parts, but is a direct continuation of 

 them. It is a dense cellular mass made up of connective tissue cells 

 aud nerve cells. In some cases it shows traces of a division into two 

 lateral halves by means of connective tissue septa which pass part way 

 into the central mass (fig. 33) . 



The connective tissue cells are numerous, rounded or slightly oval 



1 1. c. p. 54. 2 1. c. p. 56. 



