260 INVERTEBRATE MORPHOLOGY. 



As in the Eiidoprocta, a heart and a blood vascular system 

 is entirely wanting. Special excretory organs seern to "be 

 wanting in the marine Ectoprocta, excretion being performed 

 apparently by the hrernolymph-corpuscles and other meso- 

 derin- cells, especially those of the funiculus, as well as by 

 the granular cells of the stomach and csecal pouch. In Cris- 

 taiella, a fresh- water form, however, a pair of ciliated canals 

 opening into the coeloin by ciliated funnels have been de- 

 scribed, and presumably are excretory in function, the two 

 canals uniting together to open to the exterior by a single 

 pore situated between the mouth and anus. Up to the pres- 

 ent, however, these structures have not been observed in 

 other forms and apparently they do not exist in the marine 

 forms. 



In some of these latter (Alcyonidium, etc.), however, a cili- 

 ated tubular structure, which communicates at one end with 

 the ccelom and opens to the exterior between the tentacles 

 at the other, occurs and has been termed the intertentacular 

 organ (Fig. 115, io). It suggests a nephridium in its relations, 

 but apparently does not possess an excretory function, but 

 serves as an exit for the reproductive elements to the exterior. 

 In other marine forms and in all the fresh-water genera such 

 special reproductive ducts have not been observed, and the 

 mode of escape of the sexual products in these forms is still 

 unknown. Many of the Ectoprocta are hermaphrodite, the 

 ova and spermatozoa (Fig. 115, ov, te) arising from the peri- 

 toneal rnesoderm, frequently from that surrounding the 

 funiculus. Whether, however, herniaphroditisin is a charac- 

 teristic of the order or not is a point as yet undecided. 



1. Suborder PliylactolcBinata. 

 The members of this suborder are exclusively inhabitants 



/ 



of fresh water and are characterized by the tentacles being 

 arranged in a horseshoe-shaped manner (except in the genus 

 Fredericdla, where they form a circle), and by the occurrence 

 of a well-developed lobe or epistome overlapping the mouth. 



The colonies assume various shapes in different genera, 

 being sometimes dendritic and incrustiug stones or other 



