CONTRACTILE VESICLES. 71 



in the majority of the Infusoria, the contractile vesicle exhibits at the 

 period of its fullest expansion or " diastole," a merely spheroidal contour, 

 and becoming entirely lost to view at the moment of collapse or " systole." 

 The time occupied between the consecutive pulsations of this organ is 

 found, under normal conditions, to present a constant average among 

 individuals of the same species, varying from a few seconds only in certain 

 forms to over sixty or even one hundred seconds in other types. Un- 

 doubtedly, in many cases the characters afforded by the pulsations of this 

 vesicle yield a useful accessory feature for specific diagnosis, and the regis- 

 tration of such characteristics, in connection with the technical description 

 of each specific form, would be of value. Passing on to the more complex 

 phases of this structure, reference may first be made to those types in which 

 the otherwise simply spheroidal contractile vesicle is supplemented with 

 two or more lateral sinuses or lacunae, the contents of which flow together 

 immediately upon the contraction or systole of the central vacuole and 

 assist materially in the re-expansion of this central part. An instance in 

 which two symmetrically bilateral accessory sinuses are combined with 

 a central vesicle, exhibiting in this case a broadly pyriform outline, has 

 been ascertained by the author to occur in Urocentrum turbo, a similar modi- 

 fication being likewise characteristic of the homomorphic species Calceola 

 (Peridiniitm] cypripedium of Professor H. James-Clark. Examples in which 

 a greater and variable number of similar lateral or peripheral sinuses are 

 found along with the central vesicle, imparting to it under certain conditions 

 a characteristic rosette-shaped configuration, are afforded by such forms as 

 Follicularia ampulla, Trachelophyllum apiculatum, and Didinium nasutum. It 

 is, however, in such types as Paramecium aurelia and Ophryoglena flava that 

 this special modification of the contractile vesicle attains its most complex 

 development. Here, it is found that the supplementary sinuses present a 

 narrower or more linear contour, and exhibit, as a consequence of their 

 radiate plan of disposition around the central vacuole, an elegant and highly 

 characteristic stellate aspect. In Paramecium there are usually from five 

 to seven or eight of such radiating sinuses, while in the case of OpJiryoglena, 

 Lieberkuhn has reported the existence of no less than thirty. Examined 

 carefully with the assistance of the higher powers of the microscope, it has 

 moreover been demonstrated by the authority last quoted, and also by 

 Mr. Carter, that these lateral sinuses extend as slender radiating and 

 frequently branching canals throughout the entire cortical layer. A still 

 more conspicuous canal-like system that anastomoses with a main or 

 central contractile vacuole, may obtain. This special type of organization, 

 while occurring in a considerable number of infusorial forms, is perhaps 

 most prominently illustrated by the various representatives of the genus 

 Stentor. Here, the main and spheroidal dilatation of this organ is situated a 

 little below the peristomal ciliary wreath, to the left hand of the ventral 

 aspect, and closely adjacent to the anal aperture. From this spheroidal 

 dilatation, as first pointed out by Lachmann, a single long and more or less 



