ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 389 



Embryology of Cestodes.* — Prof. B. Grassi and Dr. G. Kovelli begin 

 by discussing the developmental cycle of Cestodes. They find that 

 Tssnia ellipiica has an intermediate host in the flea of the Dog and 

 of Man, as well as in Tricliodectes. They do not accept the doctrine of 

 Megnin that T. serrata can develope without an intermediate host. On 

 the other hand they are certain that T. murina of Mus decumanus 

 developes without an intermediate host, though not without a cysticer- 

 coid stage ; to demonstrate this it is necessary to make use of white 

 mice three to four months old. Moniez and Linstow are correct in sup- 

 posing that the cysticercoid found in Tenehrio molitor is that of T. micro- 

 stoma ; it is not that of T. murina. As has been already shown, T. nana 

 has also a distinct mode of development, and indeed this is only a 

 variety of, even if it be not distinctly the same as T. murina. Of the 

 tapeworms of fowls, T. proglottina has an intermediate host in Limax 

 cinereus, L. agrestis, and L. variegatus ; T. infundibuliformis in the house- 

 fly, and T. cuneata in the earthworm Allolobophora foetida. T. leptocephala 

 of the rat has an intermediate host in several insects, of which the most 

 ordinary appear to be the lepidopterous Asopia. Parona was right in 

 regarding the perch as the other host of Bothriocephalus latus. 



The authors have set before themselves three morphological pro- 

 blems: — (1) To determine why the scolex of the cysticercus (and 

 probably also of the cysticercoid) is developed as hollow and invaginated ; 



(2) To see whether the embryology of Cestodes affords new arguments to 

 support the view of an af&nity between them and the Trematodes ; and 



(3) To put in a clearer light the development of the organs of Cestodep. 

 The larv£e of Cestodes may be arranged in three chief groups : there are 

 cysticerci with inconstant invagination and no embryonic coverings 

 (Arcliigetes) ', cysticerci with later invagination {Tsenia elliptica and 

 T. murina) ; these may be again subdivided, for the invagination may be 

 simple (T. elliptica), or it may follow the formation of embryonic 

 coverings (T. murina') ; thirdly, there are cysticerci in which the 

 invagination is early, and is succeeded by the formation of embryonic 

 coverings (cysticerci in the strict sense). 



The authors are of opinion that the development of the invaginated and 

 hollow scolex is explicable by cenogeny and the better development of 

 the embryo (as by the formation of special envelopes) in agreement with 

 the great power of regeneration which is possessed by the body of 

 Cestodes. 



As to the relationship between the Cestodes and the Trematodes 

 the authors have shown that the cercariaeform period, which was believed 

 to be confined to a few forms, is very common, and its significance is 

 very high ; in the Tseniidse there have been found distinct signs of a 

 foregut (oral cavity and pharynx separated from it by a constriction) ; the 

 primitive cavity is comparable to the mesenteron of Trematodes. It must 

 be remembered that in the Cestodes, in correlation with the disappearance 

 of the sensory organs and mesenteron and the want of a blood-vascular 

 apparatus, development is much abbreviated, and the differentiation of 

 germ-layers is very incomplete ; indeed, there is but a single mass of 

 cells (blastema) from which all the organs arise. It is possible that the 

 six-hooked embryo consists only of ectoderm, although against this we 

 must set Lang's discovery of the endodermal origin of the gonads of 



* Centralbl. f. Baktcriol, u. Parasftenk., v. (1889) pp. 370-7, 401-10. 

 1889. ■ 2 E 



