ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 571 



Cystic Stages of Taeniadae.* — A. Villot fimlB, as ii result of pro- 

 longed iiKiuiries into tlie cliaraeters of tlie cystic stages of Tape- 

 worms that the mode of formation of the head is identical in all 

 species, genera, and types. The true head, the future scolcx, never 

 proceeds directly from the caudal vesicle ; it is always separated from 

 it by an intermediate portion, which ho has called the body, and 

 which forms its immediate envelope. The differential characters 

 which can be drawn from the modifications in structure and develop- 

 ment have only a secondary value and cannot be used as the basis of 

 a natural classification. In the next place, it is to be (observed that, 

 contrary to what is ordinarily taught, the caudal vesicle of the cysti- 

 cerci may bo formed in different ways; these ditt'erences have a future 

 morphological importance. Cysticerci are either cysticerci properly 

 80 called, or are cysticercoids ; the latter may be grouped under two 

 heads and subdivided into six entirely new genera. The first section 

 consists of those in wliich the caudal vesicle is formed by endogenous 

 gemmation, and here we have Polycercus for tlie form found by 

 Metschnikoff in Lumhricus terrcslris, Mowjcercus for the so-called 

 Cysticercus arionis ; in the second section, or that of those in which 

 the caudal vesicle is formed by ex(jgcnous budding, we have Cercocystis 

 for the form found in the larva of Tenehrio molitor, Stapliylocyslu for 

 S. bilariua and S. micr acanthus, Uroryslis for a form found in Glomeris, 

 and Cryptocystis for the curious form found by Metschnikoff in the 

 visceral cavity of Trichodectes canis. 



The forms that are the most ancient and most closely approximated 

 to the primitive type appear t(j be those that belong to tlie genera 

 JJrocyslis and Cryptocystls ; it is in these that wo observe the greatest 

 independence between the difl'ercnt stages of development ; the 

 proscolex, cystic, and scolex-stages are perfectly distinct ; the first, 

 after having budded off the caudal vesicle separates from it, so soon 

 as it has attained maturity, and no part of the proscolex is found in 

 the perfect cysticercus. In StayhylocAjstis and Cercocyslis the caudal 

 vesicle adheres to the blastogeu, but has only the function of a 

 support or simple appendage. In the first section of the cysticer- 

 Cfnda the blastogen not oidy persists, but f(jrrns a permanent envelop''. 

 In passing from the cysticercoids to the true cysticerci we advance 

 another stage in the scale of differentiation, and, at the same times, note 

 a remarkable abbreviation in the history of development, for the stage 

 represented by the budding of the caudal vesicle is entirely sup- 

 pressed. This " serial co-ordination " of the cystic stages may be 

 expressed by the simple law that the most differentiatc<l tyfies of 

 organization have their develoi)meiit the most condensed ; those that are 

 relatively lower are more difi'nsed ; in other words, the complieution oi 

 development and of organizaticjii are in inverse relation to one another. 



Anatomy and Development of Trematoda.t— J. l''i<jhringer devotes 

 the great«;r part of this essay to sporocyst-stages, and has investi- 

 gated the charaetei's of (Jcrrarin (irtiiaJa, C. mnn-'Kterra, (J. niinura, 



" Ann. H.i. Nat.— Zool., xv. (1883) art. No. 4. Gl pp. (1 pi ). 

 t Arb.it. Zo.<l. In^t Wiiizlnirif, vii. (1884; pp. 1-28 (I pt) 



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