504 ON TWO REMARKABLE SPOROCYSTS, 



clear and bright appearance in the living condition, so that they 

 are very conspicuous even under a low power. These, which are 

 separated from one another by very regular intervals, are all 

 connected with the lateral filament, usually by means of side- 

 branches, sometimes (rarely) directly with the main filament itself, 

 which then seems to pass through them. There is no direct 

 evidence of the nature of these filaments of the lateral line; but 

 from the way in w^hich they branch I have very little doubt that 

 they ai-e nerves. If this should prove to be correct, the regularly- 

 arranged cells connected with them, though they have no processes 

 projecting on the exterior, are probably sense-cells of some sort. 



Applied to the inner surfaces of the bundles of longitudinal 

 muscular fibres are a number of very large granular cells about 

 0-04 mm. in diameter, with vesicular nuclei O'Ol mm. in diameter. 

 As shown by their relations and their developmental history 

 these are the myoblasts of the longitudinal muscular fibres. 



The branches of the tail resemble the tail proper in structure, 

 except that the transverse fibres are more irregularly arranged and 

 closer together. In the lobed disc at the proximal end of the 

 trunk the bundles of longitudinal fibres become spread out so 

 as to be inserted into the lobes. The dorso-ventral bundles are 

 here represented by thick columnar cells. 



Not much attention appears to have been paid to the structure 

 of the tail in Cercaria; but, so far as I am able to judge, the 

 form at present under consideration would appear to be excep- 

 tional in this respect, especially with regard to the entire absence 

 of any axial strand. Thus Leuckart states (6, p. 512): "Unterhalb 

 der Cuticula erkennt man deutliche Rings- und Liingsmuskeln 

 und das nicht bios am Rumpfe, sondern auch am Schwanze, nur 

 dass sich letztere hier gewuhnlich rechts und links zu breiten 

 Bandern gruppiren, und somit eine Anordnung zeigen die man 

 bei aufmerksamerBetrachtung schon aus der entschieden seitlichen 

 Beweoungen des Schwanzes erschliessen konnte. Die Zellen des 

 Achsenstranges sind in eine glashelle Bindesubstanz verw^andelt 

 die nur noch einzelne spindelformige Korper erkennen lasst und 

 nach Art eines (unvollstiindig erhiirteten) Skelettes dazu dienen 



