RHABDOCOELA. 219 



Fam. 1. Proporidae. With one generative opening, without accessory female 

 apparatus ; with soft penis. Proporus v. Graff, Proporus venenosus 0. Schm., 

 Plymouth; Monoporus v. Graff, M. rubropunctalus 0. Schm., Plymouth. 

 Haplodiscus Weldon. 



Fam. 2. Aphanostomidae. With two sexual openings, the female being 

 anterior to the male. With bursa seminalis and soft penis. Apkdnostomum 

 Oersted, A. diversicolor Oe. , A. elegans Jen., Plymouth ; .Nadina Uljanin ; 

 Cyrtomorpha v. Graff; Convoluta Oersted, C. paradoxa Oerst., English coast, 

 etc.; Amphickoerus v. Gr. ; Polychoerus. 



Order 2. RHABDOCOELA. 



With straight, rod-shaped enteron, and protrusille pharynx. 



This order includes the smallest forms in the class, but not the 

 most simply organised. On the contrary, the structure of the 

 parenchyma lends support to the view that they are the most 

 highly organised of the class. The enteron is unbranched, and lies 

 in a space simulating a body-cavity. The vitellarium is sometimes 

 not separated from the ovary. They live on the juices of small 

 worms and of the larvae of Entomostraca and Insecta, which they 

 envelop with a cutaneous secretion containing rhabdites, and after- 

 wards suck. They are mostly fresh-water, but a few of them are 

 to be met with in the sea, and some upon land (Prorhynchus sphyro- 

 ceplialus). Parasitic forms are also known (Grafilla muricicola in 

 the kidney of Murex Irandaris, Fecampia erytlirocepliala in gut of 

 Carcinus maenas, etc.). 



Fam. 1. Macrostomidae. With two generative openings, the female being in 

 front of the male. Without accessory female apparatus ; with simple pharynx. 

 Mecynostomum E. v. Ben., marine ; Mctcrostomum E. v. Ben., f.w. and mar., 

 M. hystrix Oe., f.w.; Omalostomum E. v. Ben., marine. 



Fam. 2. Microstomidae. With sexual and asexual reproduction ; with 

 simple ovary, without accessory female apparatus ; with simple pharynx. 

 Microstomum 0. Schmidt, dioecious, f.w. and mar., M. lineare Oe., f.w.; 

 Stenostomum 0. Schm., dioecious, f.w. and mar., S. lemnae Dug., S. leucops 

 0. Schm., f.w.; Alaurina Busch, hermaphrodite with follicular. testes, A 

 Claparedii v. Graff, coast of Skye. 



Fam. 3. Prorhynchidae. With separate generative openings, the female 

 being ventral, the male combined with the mouth. With simple ovary divided 

 into germarium and vitellarium ; with variable pharynx. The so-called pro- 

 boscis is the copulatory organ. Damp earth or fresh water. Prorhynchus 

 M. Schultze, P. stagnalis M. Sch. 



Fam. 4. Mesostomidae. With one or two generative openings ; vitellarium 

 and germarium either distinct organs or separate parts of the same organ. 

 Usually with accessory female apparatus, and always with compact paired testes. 

 With a ventrally-placed rosette-shaped pharynx. F.w. and mar. Otomesostomum 

 v. Graff; Mesostomum Duges (Fig. 168); Bothromesostomum'bL Braun ; Castrada 

 O. Schm.; Promesostomum v. Gr., P. marmoratmn Schultze, coasts of Britain; 



