Henn: South American Pceciliid Fishes. 101 



and of P. caudomaculatus from the right. A variant is sometimes found 

 which moves the anal on the side of the body opposite that which is 

 characteristic of the species. 



The males of P. caudomaculatus and C. decem-maculatus are, accord- 

 ing to Philippi, sexually active throughout the year. In the aquarium 

 they follow other specimens about continually, even though these are 

 immature individuals of either se.\. That this is not due to playful 

 instincts, or to similar reasons, is shown by the constant folding and 

 unfolding of the anal and the restless swimming up to the other fishes 

 from below and behind, which are characteristic actions of breeding 

 males. Females however show a definite rest-period, which in Berlin 

 happens during the winter. At this time one of the females under 

 observation sank to the bottom of the basin, where it remained sur- 

 rounded by the waiting males, but free from their attacks, since these 

 must rise upward from below in order to effect a transfer of the sperm. 



Aggregations of Sperm, or " Spermozeugmata." 

 A slight pressure upon the abdominal wall of narcotized male fishes 

 causes expulsion of the sexual products (Philippi). These consist of 

 numerous milk-white bodies, which stick fast to the first available 

 object. These collections of sperm are elliptical in shape and measure 

 in P. caudomaculatus 122 microns in length and 73 microns in width; 

 in C. decem-maculatus they are 220 microns long and 107 microns 

 wide. 



By fixation and staining with haematoxylin-eosin they are seen to 

 consist of closely crowded spermatozoa, the long axes of which are per- 

 pendicular to the surface of the body. The heads of the spermatozoa 

 lie at the periphery, while the center is composed of the tails and 

 a few heads of spermatozoa. The whole mass is held together by a 

 sticky substance, which is acquired in the lumen of the testicle. This 

 sticky material probably causes the sperm-body to fasten to the genital 

 papilla of the female. The entire outer portion of the genital tract of 

 the breeding male is filled with these elliptical capsules. For similar 

 aggregations of sperm in insects, which likewise lack an externa! 

 investment, Ballowitz (1895, p. 458) has proposed the name " spermo- 

 zeugma," plural " spermozeugmata.'' 



Although the spermatozoa are ejaculated in the masses called sper- 

 mozeugmata, the latter are never found in the oviduct. A number 

 of these sperm-masses, immediately after being taken from the male. 



