ZOOLOGY AND BOTANY, AIICKOSCOPY, ETC. 79 



being periodically discharged into the water. This is independent of 

 the passage of ffeces by the snail. 



The cercaria consists of a body and a Y-shaped locomotor tail 

 (furcocentrous). It is the only infective stage. They penetrate the 

 skin and the mucous membrane of mouth and gullet. All stages of 

 entry were observed. They pass to the portal system. Figures are 

 given of all the phases from the cercaria before it enters its definitive 

 host to the paired egg-producing adults two months later. A certain 

 number probably enter the blood-stream direct, while others pass first 

 through the lymphatic system. 



Eohinoderma. 



Present-day Crinoids.* — Austin Hobart Clark has published the first 

 part of a monograph on existing Crinoids. It deals with the general 

 structure of the Crinoids, and with Comatulids in particular, and is pre- 

 ceded by an introduction, a history, and a glossary. Because of the 

 extraordinary completeness of the palseontological record and the small 

 number of recent species hitherto known, the Crinoids have been studied 

 too much from the palteontological side, but the author emphasizes the 

 present-day abundance of species and individuals alike, and the im- 

 portant part tliey play in the ecology of the floor of the sea in certain 

 regions. A detailed account is given of Crinoid structure, especially as 

 regards the skeleton, and the author defends his startling theory that 

 Echinoderms are related to Crustaceans, and to barnacles in particular. 



Revision of Palaeozoic Stelleroidea.f — Charles Schuchert has made 

 an important revision of the Palaeozoic Asterids, and has also dealt in 

 part wit.h the Auluroidea from which the true Ophiuroidea arose, 

 probably in late Devonian times. Seven families of Palaeozoic Asterids 

 are recognized, which seemingly had their origin in Hudsonaster or some 

 form like it. The family Hudsonasteridaj represents the primitive stock. 

 The genus Hudsonaster includes small rigid Asterids with few and com- 

 paratively large ossicles, nearly all of which belong to the primary 

 skeleton. They are massively and simply built, with the spines rudi- 

 mentary and restricted to the adambulacrals and inframarginals. From 

 Hudsonaster the evolutionary tendency was to get rid of the rigidity 

 and ponderosity through the comparative reduction in size of the plates 

 and the introduction of many smaller secondary pieces, along with an 

 abundance of spines. Other tendencies were towards elongation of rays, 

 with greater flexibility and greater power of locomotion through the 

 indefinite dupUcation of pairs of podia, and increase of body cavity in 

 three different ways. This took place through the development of 

 interbrachial areas (a) by the inward crowding of the single inter- 

 brachial axillaries, followed by more and more pairs of proximal infra- 

 marginals ; {h) through the insertion of an indefinite number of accessory 

 ossicles between the adambulacrals and the inframarginals, forcing the 

 latter more outward ; and (c) through the introduction of supernumerary 



* U.S. Nat. Mus., Bull. No. 82, pp. 1-406 (17 pis. and 513 figs.). 



t Smithsonian Inst. U.S. Nat. Museum, BuU. No. 88 (1915) pp. 1-311 (33 pis.). 



