ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 181 



Each spicule has its musculus exsertor, which is not a single muscle, 

 but is composed of two components, — a plicator and a fixator of the 

 sheath. 



The lateral nerves and the dorsal nerve end in common in a caudal 

 ganglion, which lies about the middle of the tail. From this in each 

 lateral line a fine nerve-strand runs for a short distance backwards, 

 innervating a somewhat lateral simple papilla. On the dorsal wall of 

 the hind-gut, behind the anal ring, a nerve-strand runs backwards from 

 the ring to the caudal ganglion. 



Platy helminthe s . 



Echinococcus alveolaris.* — 0. v. Linstow has reinvestigated this 

 form from a pig's liver, which used to be regarded as a tumour (an 

 alveolar colloid neoplasm). Many regard it as a distinct species of 

 Echinococcus, but von Linstow gives good reasons for interpreting it as 

 .an abnormal modification of Echinococcus polymorphic It arises from 

 a form which has been smothered in hepatic tissue and half -starved. 

 The scolex-formation is sparse or absent, and the number of hooks, 

 which should be about thirty-six, may sink to ten. Von Linstow also 

 describes Plerocercus lachesis sp. n., a Cestode from Lachesis mutus. 



Triplotaenia mirabilis.j — J. B. V. Boas describes a remarkable new 

 tapeworm from the intestine of a " rock-kangaroo " (probably PetrogaJe 

 joenicillatci). It consists of a scolex (with four suckers and no hooks), 

 bearing two long puckered bands or strobilse, in which the proglottides 

 are not demarcated and the gonads occur in closely crowded succession. 

 The presence of three shell -envelopes and of a pear-shaped process from 

 the innermost envelope suggested relationship with the Anoplocephalinse. 

 The unarmed head is another resemblance, and the unilateral position 

 of all the genital apertures brings this new form near the genus Anoplo- 

 cephala. All the tapeworms hitherto described from Marsupials have 

 been Anoplocephalinse. 



As four similar specimens were obtained, there can be no question 

 of abnormality. It is true that abnormal Cestodes with lateral chains 

 springing from the main chain have been described, but here the main 

 chain is undeveloped and the accessory chains spring from the scolex. 

 Another peculiarity is the absence of distinct proglottides, which some- 

 times occurs as an anomaly elsewhere. A third peculiarity is the dif- 

 ference between the two sides of the chain ; one side is smooth and 

 swollen, the other is thin and puckered, — a condition somewhat like 

 that of Tamia villosa from Otis tarda. 



Cysticercus fasciolaris.J — E. Bartels gives in the first place an 

 account of the structure of this bladderworm of the mouse, which 

 hardly differs from the structure of the tapeworm of the cat (Tcenia 

 crassicollis) except in the absence of a terminal excretory bladder and 

 •of any hint of gonads. Even the jointing or segmentation is quite 

 pronounced in the Cysticercus-stage. He describes successive stages in 



* Zool. Anzeig., xxvi. (1902) pp. 162-7 (14 figs.). 

 + Zool. Jahrb., xvi. (1902) pp. 329-34 (1 pi.). 

 X Tom. cit.,pp. 511-70 (3 pis. and 2 figs). 



