230 SUMMARY OP CURRENT RESEARCHES RELATING TO 



found in Thuringia. In all individuals of this species cilia may bo 

 distinctly made out over tho wholo of tbo body ; at various points aro 

 groups of stiff setaj three or four times as long as the ordinary cilia, and 

 to such Lang has correctly ascribed sensibility. The excretory canals at 

 the anterior end of the body are very distinctly seen, owing to the slight 

 development of pigment, and the absence of other opaque organs ; tho 

 lateral primary canals arc much coiled, and lie above the intestine ; 

 they pass forwards externally to the eyes, and soon unite with one 

 another, just as in Dendrocadum lacteum ; a number of the elongated 

 ciliated funnels are set alone on the finer branches of the system. The 

 author is of opinion that P. ulvae Oersted should be placed in the genus 

 Gunda, and the arrangement of its generative organs agrees exactly with 

 what is seen in G. segmentata Lang. The penis of P. abscissa is much 

 smaller than in other species, and there is no swelling on the course of 

 its duct ; between the lining epithelium and the external muscular fibres 

 there are circular muscles ; the great development of the muscles in the 

 wall of the penial sheath may be correlated with the absence of a portion 

 formed of coiled fibres, which is of great importance in the ejaculation of 

 the sperm. 



In P. torva the numerous testes are arranged in two layers, above 

 and below the enteric branches, just as the author has described them 

 in Dendroccelum lacteum; in the other species examined they are in 

 one layer, dorsal in P. gonocejphala, P. polychroa, and Gunda ulvse ; in 

 P. abscissa they are ventral in position. 



In P. torva and P. abscissa the two oviducts unite, above the penial 

 sheath, into a common duct which opens, in the former, above the top of 

 the penis, and in the latter, just internally to the opening of the penial 

 sheath. In P. gonocepliala, as in P. polychroa, each oviduct opens 

 separately into the terminal part of the uterine duct ; the unpaired duct 

 of G. ulvse opens at the same point. 



In addition to the two ventral longitudinal nerves there are two 

 much more delicate lateral nerves ; these arise a short distance in front 

 of the eyes, and it may, therefore, be supposed that they do not take 

 their origin directly from the brain. Like the ventral nerves, they are 

 not only connected with one another by finer branches, but they give off 

 laterally plexus-forming nerves, which probably become connected with 

 the ventro-lateral nerves at the margin of the body, and so complete 

 a nervous tube, such as has been described by Gaffron in Distomum 

 isostomum. In P. abscissa and G. ulvse Dr. Ijima has been able to see 

 the so-called marginal nerve discovered by Lang. The stepladder- 

 like transverse commissures of the peripheral nervous system of P. 

 gonocephala make so many branchings and crossings, that it was 

 scarcely possible to determine their number ; in P. torva and P. abscissa 

 they are much less numerous, and yet there are more than forty of 

 them. 



The central lobes of the two just mentioned species are distinguished 

 from those of Dendroccelum or Polycelis by the fact that each is traversed 

 in the dorsoventral direction by a large column of ganglionic cells and 

 muscular bands, with which a small amount of connective tissue may be 

 connected. It may be regarded as an arrangement by which a number 

 of ganglionic cells are brought into closer connection with the inner 

 portions of the lateral parts of the brain. The brains of these Planarians 

 are also distinguished by the backward and lateral course of the lateral 



