Introduction to A nimal Morphology. 1 5 9 



(Dendroccela). The female organs consist of ist, a 

 germ-gland secreting the central part of the egg; 

 2nd, one or two yelk-glands secreting a cellular ma- 

 terial, not homologous with true yelk, which contri- 

 butes chiefly to the formation of the embryo. These 

 may open separately or in common into the oviduct, 

 which is at one part dilated into a uterus, where the 

 eggs accumulate and begin to develop. To this is 

 added a shell-secreting gland and an external duct or 

 vagina, often with a dilatation for the reception of the 

 semen (spermatheca). The male organs in Rhabdo- 

 ccela consist of a pair of pouch-like testes, with ducts 

 opening in seminal vesicles, and ending in a perforate 

 cirrus or penis, armed with recurved hooks, and, 

 when retracted, contained in a sac. In Dendroccela, 

 many vesicular testes exist scattered through the 

 body, sometimes in pairs (Bipalium). In Convoluta, 

 some individuals have developed male and rudimental 

 female organs, and others the reverse, leading us to 

 the dioecious forms (Microstomidae, Acmostomum 

 dioicum, Nemertinea, Planaria dioica). The sex- 

 organs of Nemerteans are simple follicles between the 

 intestinal caeca, opening laterally by pores above the 

 lateral nerves. The spermatozoa are rod-like. The 

 ova are rapidly developed ; sometimes several embryos 



from one egg. In some cases (Borlasia), the 



stomach cavity appears to form_by invagination 



(Ilubrccht}. In other Nemerteans, the embryo forms 



of one layer (blastula), which becomes 



ciliu.tr<l, free, and th-n by invagination becon 



ula.* In Nemertinra,".th.- soft-shell. <! egg* aiv 



The blast ula sta^'c prco rfed triple! .lactic planula st.iC in 



.ns, Amphioxu-, &c., .. 

 describes Planaria as a true dibhstuln. 



