CONTINUED DEVELOPMENT OF THE HEAD AND NECK. 



505 



Fig. 282.— Metamorphosis of the 

 head-process into the head proper 

 iu Cysticercua cellulosce. { x 20.) 



were at the end of the blind process. It sometimes happens, too, that 

 the floor of the cavity (Fig. 281) becomes intruded like a boss, and 

 thus comes to present an appearance which Moniez erroneously- 

 regarded as the formation of the tape- 

 worm head (p. 354). It is not this boss 

 which forms the head, but the whole 

 lower end of the head-process — a portion 

 so conspicuous that it includes almost 

 the whole portion which is bent to the 

 side. 



During the development of the later 

 head the process has been continuously 

 increasing in size. The receptacle, too, 

 has gradually grown to a length and 

 breadth of 1-3 mm. or more. The histological development is now 

 complete. One can recognise not only the characteristic musculature 

 of the suckers and of the rostellum, but may also distinguish the 

 muscular fibres running in various directions. In suitable pre- 

 parations the vascular system is perfectly distinct. It consists of 

 four longitudinal stems, which give off several lateral twigs, and are 

 connected together between the rostellum and suckers by a circular 

 vessel. Similarly the hooks gradually attain complete development. 

 Not unfrequently one sees round about them small isolated points, 

 the remains of the primitive spines (p. 352). 



With this process the development of the bladder-worm essentially 

 ends. The changes which afterwards ensue, after the course of the 

 second month, mostly concern only the upper 

 portion of the head-process, which is attached 

 to the still continuously growing bladder- 

 wall. This neck-like portion at first hardly 

 predominates over the enlarged lower portion, 

 hut after the formation of the head proper it 

 begins to grow rapidly, and, by the formation 

 of numerous calcareous corpuscles,^ to pre- 

 seut continually a more distinct anatomical 

 contrast to it. In other words, the de- 

 velopment of that cylindrical body begins, 

 which is usually intercalated between the 

 head and bladder - wall, and which resembles 

 the subsequent tape -worm body to such an extent that one may for 

 a while consider the two as identical. The growth progresses both 



' Moniez is mistaken in disputing the existence of calcareous corpuscles in this worm, 

 "Essai, &c.," loc. dt., p. 57. 



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Fio. 283.— Completion of 

 the head formation in Cysti- 

 cercus celiulosce. (x 15.) 



