FORMATION OF PROGLOTTIDS IN CROSSOBOTHRIUM. 207 



portion of long-necked specimens are always found when any 

 large number of the individuals of this species is examined. This 

 is borne out by the observations of some of my colleagues on 

 the staff of instruction at the Marine Biological Laboratory, who 

 have frequently observed such individuals among the specimens 

 used by the students. In this connection it may be said that all 

 the specimens which have been examined by these men, by Linton 

 and by myself have been taken between June I 5 and September 

 15. Since the sand sharks are not present about Woods Hole 

 from November to June (Smith, '97, p. 89) one could not obtain 

 data throughout the year. It would, however, be desirable to 

 examine the worms from sharks taken as late and as early as 

 possible, for there may be seasonal relations such as obtain in 

 the period of maturity in other forms, 1 and one might find at 

 another period a relatively larger number of "long-necked" 

 forms. 



III. DETAILED ACCOUNT OF THE PROGLOTTID FORMATION. 



() Material and Tcc/iniqnc. - - The C. laciniatiiin from which 

 the data here presented have been obtained were collected at 

 Woods Hole, Massachusetts, during several summers (i9O2-'o4). 

 I have examined a large number of specimens which have accu- 

 mulated since I began work upon this form and by selecting out 

 the different stages have been able to demonstrate every step in 

 the history of the strobilla with an abundance of material. In 

 some cases, the specimens were killed under the pressure of a 

 cover slip, but for the most part they were taken from lots which 

 had been killed by placing for a moment in fresh water and im- 

 mediately transferring to the killing fluid. All the material used 

 in this study was fixed in saturated sublimate with 5 per cent, 

 acetic. Almost any good stain will bring out the division lines 

 between proglottids, but for determining the location of the re- 

 productive organs in whole mounts Partsch's alum cochineal 

 gave most excellent results. 



(b] Proglottid Formation in tlie Larval Won/is. Out of an 

 abundance of material, I have been able to demonstrate again 

 and again that, in the case of young worms which have presum- 



1 See the remarks of Braun, p. 1461, upon the " time of reproduction," etc. 



