A GROUP OF TURBELLARIA. 49 



Catenula lemnae (Ant. Dug.). 



Occurs in ponds and lakes, and often appears suddenly in 

 considerable numbers in collections of rain-water during the 

 spring and summer, and disappears as rapidly as it comes. 

 It is white and thread-like in appearance, consisting of a chain 

 of 2 4 individuals (rarely more) and attaining a length of 

 5 mm. The body possesses a well-defined head lobe, which is 

 marked off by a slight constriction and a ring of comparatively 

 long cilia ; a statocyst is present. The usual mode of repro- 

 duction is by fission, but sexual organs are developed when the 

 pond or ditch begins to dry up. 



Microstomum lineare (Mull.) (PI. 4, fig. 3). 



This species is very similar to the foregoing, but the colour is 

 yellowish or greyish brown. It is usually found in the form of 

 a chain of zooids of which there may be as many as 18. The 

 colony attains a length of 8 mm. Each zooid develops a pair of 

 red eyes, behind which may be seen the ciliated pits. The skin 

 is thickly clad with cilia. No rhabdites are present, but 

 nematocysts, similar in form to those of Hydra, are present (20). 

 The figure shows the manner in which new individuals arise, and 

 various stages in the formation of mouths may be seen. The gut 

 is common to all the zooids in the chain, until fission takes place. 

 The writer has seen desmicls which had been swallowed for food 

 pass along the common gut from one zooid to another. Sexual 

 organs are sometimes produced, and the ripe eggs are oval in 

 shape and orange or dark red in colour. 



This species is fairly common in stagnant or slowly moving 

 water. It has been found in thermal springs at a temperature 

 of 130 F. and also in brackish water. It moves slowly on a 

 surface, but is a graceful and swift swimmer. 



Dalyellia viridis (G. Shaw) (PI. 4, figs. 1 and 2). 



Examples of this species attain a length of 5 mm., and are 

 generally spinach-green in colour. The colour is due to the 

 presence of algal cells Which lie beneath the epidermis. The 

 body is truncated in front, widens towards the middle and 

 then tapers towards the tail. There are two bean-shaped eyes. 

 There is a very distinct pharynx and the gut is sac-like. 



Journ. Q. M. C, Series II. No. 72. 4 



