94 DEVELOPMENT $F THE ENOPLA. 



scolex, yet he neither mentions having seen the one form inside the other nor figures this inter- 

 esting condition. No such mode of development has ever been seen by me, either in the case of 

 those ova deposited in the unimpregnated condition or in those developed within the body of the 

 parent ; but the same gradual changes ensue in the young of this animal as in Tetraslemma, and, 

 as will afterwards be seen, also in Cephalothrix. 



Many of the parents with developing young in their interior are feeble, and almost in a 

 decaying condition inside the sheaths, so that the inert bodies seem but the nidi for the growth 

 of their progeny, each of which, provided with two boldly marked eyes, and other differentiated 

 tissues, revolves rapidly within its capsule. The evolution of the ova in these decaying adults is 

 a feature analogous to the elaboration of the respective generative products in the headless frag- 

 ments of male and female specimens of Lineus marinus and others, — the last efforts of the parental 

 tissues being devoted to the reproduction of the species. 



Dr. Max Schultze was the first to describe a viviparous species (his Tetrastemma obscurum). 

 He states that in the development of the proboscis in the young animal the marginal stylets 

 appear before the central, and as the worm grows older he figures it with two loose stylets in 

 the pit of the proboscis, an arrangement, as he supposes, for the supply of the central 

 organ. I have also seen a loose stylet or two lying in the anterior chamber of the proboscis, but 

 this occurred both when there was and when there was not a stylet on the central apparatus. 

 The physiology of that region, as previously explained, demonstrates that there is no connection 

 between the marginal and central stylets, except, perhaps, in the composition of the fluid with 

 which both are bathed. Professor Keferstein next detailed the development of Prosorhochmus 

 Claparedii, a species in which the young attain considerable advancement before extrusion, for 

 they are found with four eyes, a well-developed proboscis, and other organs in the body of the 

 parent, and on being set free have the same general form as the latter (Plate II, fig. 4). M. 

 Claparede subsequently made a few remarks on the same species, mentioning that he had seen 

 specimens with ova in the sacs, but they were never numerous. By the examination of this 

 species I have been enabled to confirm many of the excellent observations of the two fore- 

 going authors, and to see that the development within the body is very similar to that of the 

 free ova and their products. The larger young specimens are often doubled within the parent, 

 and apparently invested by the stretched covering of the ovisac, or in large cavities produced by 

 the coalescing of many ovisacs ; at any rate, it is clear that to describe them, after the former 

 authors, as simply within the body-cavity of the worm, is not strictly accurate. It is curious to 

 see these large yonng animals moving within the body of the adult, apparently without causing 

 the latter any inconvenience. Such, then, appears to be a further stage of the type of deve- 

 lopment seen in Nemertes carcinophila, in which, after the deposition of the majority, a few 

 ova are left in the body of the parent for subsequent evolution. It remains, however, to be 

 observed whether all the ova in Prosorhochmus are so developed (in which case they must be very 

 few) or whether part are deposited at one or different periods, and the rest retained in the body 

 of the parent. It is probable, at least, if the ova are numerous, that they are not developed simul- 

 taneously, as in other forms, else the adult would be inconveniently distended, and the young 

 much compressed. 



Prom the foregoing it will be seen that the viviparous species are connected by insensible 

 gradations with the true oviparous forms. It may likewise be found that the former have a close 

 connection (if they are not identical) with the hermaphrodite species described by Prof. Keferstein 



