334 



FRESH-WATER BIOLOGY 



4 (27) Pharynx simple 5 



S (20) Protonephridia with one principal branch, median dorsal in position. 



Family Catenulidae . . 6 



Without eyes but with ciliated pits, non-pigmented light-refracting organs, and in one genus 

 a statocyst. The mouth Hes on the ventral side of the anterior end. The pharynx opens into 

 the anterior end of the intestine. Asexual" reproduction by budding, thus forming chains of 

 zooids, known for most species. Testes in front of ovary. Both testes and ovary may consist 

 of one or more lobes. 



(7) With one statocyst and pre-oval circular groove Catenula. 



But one species supposed to occur in America. 



Catenula lemnae (Anton Duges) 1832. 



Length of single specimen i mm. Rarely 2 to 4 or 

 8 zooids in a chain. DeUcate, white thread-like. Head 

 region set off by a circular groove lined with long ciha. 

 Intestine short and not continuous through chain of 

 zooids. 



Graff regards the European species C. lemnae as prob- 

 ably identical with the species which was collected in 

 the vicinity of Philadelphia and very incompletely de- 

 scribed by Leidy under the name Anortha gracilis. 

 Until further collections of the Philadelphia form have 

 been made this must of necessity be a matter open to 

 question, and C. lemnae be admitted to the list of Ameri- 

 can species tentatively. 



Fig. 591. Catenula lemnae. M) anterior end: 6, brain; eg, cili- 

 ated groove; w, mouth; j/, statocyst. X 75. (After von Graff.) 

 {B) Chain of two zooids. X 30. (After Mrazek.) 



7 (6) Without statocyst or pre-oral circular groove. With ciliated pits. . 8 



8 (19) CiHated pits well developed. Without proboscis. Stenosiomum . . 9 



9 (18) Head region not at all or only slightly set ofi from rest of body. . 10 



10 (17) Integument colorless n 



:i (14) Wall of digestive tract free from pigment 12 



