66 SUMMARY OF CURRENT RESEARCHES RELATING TO 



these very little developed. Pharynx a pharynx variabilis or plicatus. 

 Digestive tract lobular, or irregularly broadened out. All marine 

 except one, or possibly two species. (Under the AUoiocoela come the 

 genera Plagiostoma, Vorticeros, Monotus, and others.) 



The work commences with a complete list of the literature on 

 Tiu'bellarians from the time of Trembley, who, in 1744, figured a 

 black fresh-water Planarian, to that of the publication of the last of 

 Dr. Ai-nold Lang's important memoii'S last year. The list is followed 

 •by a general treatise on the anatomy and physiology of the Ehabdocoe- 

 lida. The account of the nematocysts of some forms is very interesting ; 

 their exact resemblance to those of Ccelenterata is fully borne out. 

 Microstomum linear e ajipears to be the only species which, like Hydra 

 and Cordylophora, possesses two kinds of nematocysts. The author 

 thinks he has been abfe to detect on the sui-face of the cuticle, trigger 

 bail's in connection with the nematocysts, like those in Hydroids. He 

 considers the rhabdites or rod-bodies homologous with nematocysts, 

 and refers, in connection with this question, to the nematocysts devoid 

 of any thread which occur in many Coelenterates, intermingled with 

 fully developed ones. The structure of the pharynx is carefully gone 

 into, and its different forms being of much use in classification, receive 

 various names, such as Pharynx hulbosus, P. plicatilis, &c. 



The water-vascular system has been studied by von Graff with 

 considerable success. It may consist of a single median canal with a 

 single posterior opening (^Stenostoma), or a pair of laterally placed 

 canals with a similar single opening or two separate lateral canals 

 with each a posterior opening (Derosioma), or there may be a pair of 

 openings or a single one somewhat anteriorly placed. Ciliated funnel 

 cells or flame cells, such as exist in Cestodes, Trematodes, and Triclad 

 Dendrocoeles, have been discovered by von Graff also in the Ehab- 

 docoelida. Ihey do not, however, occur in connection with the tips 

 of the ramifications of the water-vascular canals, but almost entirely 

 on the larger canals forming the networks. It is impossible here to 

 follow the work further, through the interesting sections devoted to 

 the development of Microstoma by budding, and the habits of life and 

 distribution of the Ehabdocoelida. In connection with the discussion 

 on classification, a table of the pedigree of Tui'bellaria is given, with 

 Proporus as the ancestral starting-point. In this family tree the 

 Dendrocoeles are shown as derived from Acmostoma, a new genus of 

 AUoiocoela, characterized by having a distinctly marked narrow 

 ambulacral sole, the Polyclades dii-ectly, and the Triclades through 

 Plagiostoma. The ascertained facts as to the structure of Tui-bellarians 

 seem to point even more closely to theii' connection with the Ccelen- 

 terata. The presence of two kinds of nematocysts in one of the 

 Ehabdocoela, and the possible occurrence in members of that group of 

 trigger haii'S, is a remarkable fact. Dr. Lang, believing that a part 

 of the nervous system in Dendrocoeles is truly mesenchymatous, as in 

 Ctenophora, and from other grounds, concludes with Kowalewsky 

 that the Polyclada are " creeping CcBlenterates which have many 

 points of structure in common with the Ctenophora, some with the 

 Medusae." Such being the case, naturalists wait with great impatience 



