ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 51 



it, SO far, with destruction and degradation. Most especially does tliis 

 affect the action of the reproductive elements on one another, and, 

 where a joint of a Tcenia does, as in some cases happens, fertilize itself, 

 it is absolutely necessary for the young to undergo a complete change. 



The author does not think that there is any alternation of 

 generation in the Taeniadfe ; he looks on the head of the Tcenia as 

 being merely an organ of fixation. The hexacanthid embryo forms 

 the vesicle, but the produced scolex is not a new individual, but only 

 a small part of the embryo, attached to the organ of fixation. All 

 the vitality of the embryo being diverted to the formation of the head, 

 the rest of the organism is unable to react against the influence of 

 external forces, and thus, by endosmosis, it is penetrated by liquid 

 matter. This liquid, accumulating in the central portion, disorganizes 

 it, and in time causes it to perish. The cysticercus is, then, a young 

 Tcenia ; the vesicle represents the first ring of the future chain ; in 

 most cases it disappears, without reproducing itself, after having 

 served as an organ of protection. What we call the scolex is formed 

 by the head (organ of fixation) and by a portion of the hexacanthid 

 embryo, the rudiment of the future rings, which thus come to be 

 situated between the first ring (the vesicle) and the head. 



In an extract from his work,* he says, that the " head " is to be 

 regarded as being morphologically developed at the hinder end of 

 the animal ; if this be so it is easier to compare their gemmation with 

 that which obtains in the other Vermes. 



It will be seen from this sketch that M. Moniez's views are not 

 altogether those which have been hitherto regarded as explaining the 

 history of the Teeniadse. 



Echinoderniata . 



Sexual Dimorphism in Eehinoderms.f — Prof. T. Studer brings 

 forward some evidence to show that the current opinion, which denies 

 any sexual dimorphism to creatures of this group, is not altogether 

 well founded. Investigators on Echinoderms of the Arctic and Ant- 

 arctic seas have especially revealed a number of exceptions to the 

 ordinarily accepted rule. 



In cases where development is compressed we often find the young 

 remaining for a long time under the protection of their mother. Long 

 ago (1844) Sars observed cases of this kind in Asterias Muelleri and 

 Echinaster sanguinolentus, and Daniellssen and Keren made (1856) 

 somewhat similar observations on Pter aster militaris. Wyville Thom- 

 son has increased our knowledge as regards the Asterida, and Schultze 

 and others have extended it to the Ophiurida (^Amphiura squamata). 

 Studer has himself described Ophiomyxa vivipara from the coast of 

 Patagonia. The first to observe cases of this kind among the Echi- 

 noidea was Philippi (1845), and he has been succeeded by Agassiz, 

 Studer, and W. Thomson. So again, Thomson followed Oersted in 

 discovering viviparous arrangements among the Holothuroida. The 

 cases cited fall under two heads — either the ova are developed within 



* Kev. Internat. Sci. Biol., vi. (1S80) p. 135. 



t Zool. Anzeig., iii. (1880) pp. 523-7, 543-6 (10 figs.). 



E 2 



