40 I'LATYHELMINTHES TURBELLARIA 



behind the pharynx into a receptacle lined by lon 

 columnar cells, which, however, are not all of the same kind. 

 The uterine duct opens into the atrium just above the aper- 

 ture of a problematical, eversible, " musculo- glandular organ" 

 (mgr). 



Fertilisation appears to occur in the uterus, where ova, yolk, 

 and spermatozoa, or (in P. torra) spermatophores (Fig. 14, X, sp\ 

 are found. The formation of the cocoon in Planaria lactca is 

 probably begun in the " uterus," but is undoubtedly completed 

 in the genital atrium. In P. polychrua, however, the stalked 

 cocoon is formed wholly in the " uterus." Thus we rind two 

 types of cocoons in different species of the genus Planaria 

 associated with two types of reproductive organs (Hallez) : 



I. Planariae in which the two oviducts open separately into 

 the posterior part of the duct of the uterus. A musculo-glandulnr 

 organ is absent. The cocoons are spherical and stalked. Ex- 

 amples Planaria polychroa (Fig. 14, L), P. albissima, P. 

 gonocephala. 



II. 1'lanariae in which the two oviducts open by means of an 

 unpaired duct into the genital atrium. A musculo-glandular 

 organ present (Planaria torra (Fig. 14, X), P. mrazekii, P. lactca, 

 P. cavatica), or absent (P. alpina, Fig. 14, M). The cocoons 

 are sessile. 



The genitalia of the Maricola (Fig. 14, F) and Terricola do 

 not differ very much from those of Planaria. The uterus (greatly 

 reduced in the Land Planar ians) lies behind the genital pore, 

 and several ova, together with much milky yolk, are enclosed in 

 a capsule which is formed in the genital atrium. 



Asexual Reproduction. 1 It has long been known that fresh- 

 water Planarians have not only great powers of repairing injuries, 

 but that they use this faculty in order to multiply by transverse 

 fission. Planaria alpina and Polycelis cornuta, in summer, 

 separate off the posterior part of the body, and this ultimately 

 becomes an entire individual. P. albissima, and especially P. 

 suite ntaculata, anticipate matters so far, that before fission is 

 complete, the new individual has a head nearly fully formed. 

 The new organs are largely regenerated in both parent and young, 



1 The extensive literature on this subject is fairly completely summarised by 

 Voigt iu liiol. Ccntralbldit, vol. xiv. Nos. 20, 21, 1894. Faraday's observations 

 (cf. p. 6, note 6) have been generally overlooked. 



