324 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



act as a secreting chamber, else the large ones could receive no increase after 

 they had outgrown the capacities of the globules. They seem to be formed by 

 gradual increase of layer upon layer of the calcareous glassy secretion, as is well 

 shown in some specimens mounted in chloride of calcium, where they have 

 assumed a stratified or laminated appearance. Sometimes a process (Plate IV. 

 fig. 10), probably a remnant of the globule, passes from the head down the shaft 

 of the spike for a short distance, as indicated by Dr Schultze in Tetrastemma,* 

 though seldom to such an extent in the adult stylet. The knob on the head 

 figured by this author must be rare, and probably represents a casual globule. 

 The stylets are dissolved in weak acetic acid, as first noted by M. de Quatrefages, 

 and are roughened or corroded by strong liquor potassae. 



In a large animal an interesting arrangement of the stylet-sacs occurred on one 

 side, for there were two of nearly equal size, which communicated with each 

 other at one end, so that an interchange of fluid and granular contents took 

 place. Only one had a duct of communication with the anterior chamber of the 

 proboscis. The opposite side had a single sac of the usual formation, containing 

 two large and perfect stylets, and a shorter without a head. On the abnormal 

 side the outer sac (in this view) had two fully formed stylets, a larger and a 

 smaller clear globule, besides some other minute globules and granules ; the 

 inner, which possessed the duct of communication, had one stylet as large as 

 the preceding, and fully formed ; another somewhat less, but also having a head ; 

 a third slender spike of greater length than the latter, but headless; and a 

 fourth, rather more than half the length of the last mentioned. No globule 

 existed in the inner sac. It is interesting to notice the different degrees of per- 

 fection of these spikes in relation to what Dr Schultze avers as to their develop- 

 ment, viz., that they are the products of the smaller contained vesicles. In the 

 one there were two large globules, and two perfect stylets, yet no trace of a de- 

 veloping spike ; in the other there were three completely formed stylets, yet 

 each varied in length ; while the long spike without a head was fully as long as 

 the largest in that sac— head included. The stylets in the outer sac were quite 

 as large as the central stylet. Thus at present, though I have often seen spikes 

 inside, and connected with the fluid vesicles, I cannot support Dr Schultze's 

 notion that the spikes must be developed therein. M. Claparede says he has 

 never seen the spikes inside those vesicles,! but I observe, in a more recent publi- 

 cation, % he figures a developing stylet in a globule in Prosorhochmus Claparedii. 



In a specimen that had often been under the microscope, I found on one 

 occasion a pair of stylets, apparently from the lateral sac of one side, advanced 

 nearly to the ganglionic portion of the proboscis. One lateral pouch, as it 



* Beitrage zur Naturges der Turb. tab. vi. fig. 10, a. 



t Recherches Anat., &c. p. 79. 



\ Beobachtungen iiber Anat. und Entwicklung, &c, 1863. 



