46 THE TEMNOCEPHAL01DEA 



the monogenetic (Heterocotylean) Trematodes, rather than with 

 the Turbellaria. 



But in the nervous system the Temnocephaloidea retain a 

 much more primitive condition than that presented by the existing 

 Rhabdocoelida. The extensive network arising from the brain 

 presents three main tracts on each side of larger dimensions. 



The genital organs (Fig. I. 7) are formed on the ordinary 

 Platyhelminth plan ; in their position posteriorly to the intestine, 

 and in the lateral position of the testes, the Temnocephaloidea re- 

 semble the Turbellaria. The testes retain the primitive, bilateral 

 symmetry ; but the testis of each side is so deeply constricted as 

 to form two oval, or it may be lobulated organs, connected together 

 by a narrow duct, so that there is here a commencement of that 

 process which results in the " follicular" arrangement of Tricladida, 

 and Polycladida. The penis presents a Rhabdocoelidan character 

 in being enveloped in a chitinous sheath, resembling that of many 

 tubificid Oligochaetes (such as Limnodrilus) ; while the terminal 

 region of the sperm duct is eversible, and provided with chitinous 

 spines. 



The female gonad has undergone that same differentiation into 

 germarium and vitellarium which occurs in many Turbellaria. The 

 former is compact ; the latter presents a peculiar and characteristic 

 arrangement in its reticulate structure, covering the dorsal surface 

 of the sac-like intestine. The vagina is armed. 



The whole anatomy, therefore, of the Temnocephaloidea 

 exhibits a remarkable intermediate condition between the 

 Rhabdocoelida and the Trematoda, while presenting certain 

 peculiarities of its own, which entitle the animals to a position 

 independent of these two classes. Nothing is known of the 

 development beyond the fact that the eggs are laid in capsules 

 (sometimes operculated), which are pyriform and stalked, except 

 in T. fasciata, where several oval eggs are embedded in a mass of 

 secretion. 



1. Haswdl. Quart. Journ. Mic. Sci. xxviii. 1888, > 279. 



2. Ibid. (For all previous literature.) Macleay Memorial Volume 1893, 



p. 93. 



3. Ib id. (Actinodactylella.) Macleay Memorial Volume, p. 153. 



4. Max Weber. Zool. Ergebnisse einer Reise in Niederl. Ost-Ind. 1890, vol. 



i. p. 1. 



5. Plait. SB. Akad. Wiss. Berlin, 1894, p. 527. 



