208 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



wliicli the composition of the tail by the coaptation of a superior and 

 ail inferior half is easily demon strable. 



In at least one species, however, this structure of the tail appears 

 not to obtain. In Myxoholus macrurus the structure in (luestioii seems 

 not to be a shell process at all, but an independent structure with dif- 

 ferent optical and chemical properties. Although at first inclined to 

 suspect the existence of the two lateral pieces (without the median 

 piece; see p. 250) in the untailed forms, I was unable to detect any 

 trace of them, as iodine failed to separate such a structure. Further, 

 I was unable to prove the constancy of the imtinl jjoster tor divergence 

 of the valves Avhich in M. macrurus I suspected to be correlated with 

 the described structure of the tail. 



Sporoplasm. — Correlated with tlie typical number and position of the 

 capsules is the characteristic peltate shape assumed by the sporoplasm. 

 The shape and the topographic features of this structure , are described 

 in detail under Myxoholus macrurus (p. 251). The sporoplasm contains 

 nuclei, an iodinophile vacuole, and " granules." 



Nuclei (see also "granules" below). — Tliese were first observed by 

 Thelohan. He describes^ the condition as follows: A series of spores 

 properly stained shows some with 1 nucleus (frequently situated at or 

 near the median cornua) and others with 2, 3, or 4 nuclei, everything 

 pointing to their origin by division fi'om the single one. The subse- 

 quent ones appear to migrate at first outward and then backward. 



Yacuole (iodinophile). — Although visible on some of Miiller's figures, 

 Biitschli- was the first to direct attention to this structure. He 

 descril^ed it as a nucleus, remarking that, though sometimes visible in 

 the fresh state, it became more distinct upon the addition of acetic acid 

 or iodine solution. He failed in his efforts to stain it, a result that he 

 attributed to failure of penetration through the shell of the staining 

 fluid. 



In 1889 Thelohan 3 corrected this erroneous interpretation, showing 

 that the structure in question is a vacuole. Little differentiated in the 

 fresh state (on account of similar refrangibility) from the sporoplasm, 

 it becomes evident when the latter is coagulated by alcohol, acetic, 

 nitric, or osmic acids, or by silver nitrate solution (2 per cent). Its 

 chief micro-chemical characteristic is its extreme resistance to nuclear 

 stains, which affect all the surrounding parts.^ Iodine alone stains it 

 a brownish red, the remainder of the protoplasm taking a pale yellow 

 hue. The iodine reaction exactly resembles that exhibited by glyco- 



1 Anna], de Microgr., 1890, ii, p. 210. 



^Ztsclir. f. wiss. Zool., 1881, xxxv, p. G3G. 



' Compt. Rend. Acad. Sci. Paris, cix, i)p. 919-920. For Perugia's confirmation see 

 M. merlucii, p. 243. 



■'Biitsclili, indeed, states the contrary, but my own results are throughout in accord 

 ■with those of Thelohan, as are also those of Perugia (Boll, gcientif,, Pavia, 1891, xiii, 

 p. 24). 



