MUSEUM OF COMPARATIVE ZOOLOGY. 55 



as primary egg- membranes; but Steeustrup ('63) subsequently showed 

 that the egg of Myxine glutinosa possesses this covering before it leaves 

 the ovary, from which it follows that the " horny capsule " is really a 

 primary membrane. 



Thomson's ('59) account is brief: "I have found that in the Myxine 

 glutinosa the globular yolk is enclosed in a horny capsule of similar 

 consistence and structure [to that of the oviparous cartilaginous fishes], 

 but of a simple elongated ellipsoidal shape, and in place of four terminal 

 angular tubes, a number of trumpet-shaped tubular processes projecting 

 from the middle of the two ends, which probably serve the same pur- 

 poses as the differently shaped appendages of the ova of the shark and 

 skate." 



Steenstrup ('63, pp. 233-238, Figs, a-h) also saw the horny egg- 

 shell and the peculiar projections from its ends. He says (p. 236) : 

 " In the last received individuals the eggs now had not only the same 

 considerable size [as some large eggs previously described] and more 

 oval-elliptical form, but besides they were surrounded with a somewhat 

 firmer, almost horn-like egg-shell, which was furnished at the ends with 

 a large number of slightly curved or S-shaped horn -threads. Each 

 horn-thread ends in a head-shaped portion with three or four projecting 

 spines or hooks, and has thereby some resemblance to a ship's anchor. 

 The threads recall — even though somewhat remotely — the horn-threads 

 projecting from the eggs of the rays and sharks, much as the shell itself 

 recalls the firm capsule of these cartilaginous fishes. The accompanying 

 figures exhibit both the appearance of the capsules (/, g) and the man- 

 ner in which they hang in the mesovarium (A** and A***), together 

 with eggs of the same appearance as c, d, e (Fig. A*), and with a large 

 number of only slightly developed eggs (o, o, in Fig. A)." 



In the two eggs with horny shell figured by Steenstrup, the shell has 

 been represented as though it were composed of two parts separated by 

 a sharp continuous line ; the egg appears cut through near one pole by 

 a plane perpendicular to its long axis. The appearance recalls that seen 

 in the egg-shells of certain trematodes, where one end serves as a lid 

 which opens to allow the larva to escape ; but whether the author re- 

 garded this as a similar provision for the escape of the young hag, or as 

 an accidental condition, is not stated in the text. 



Wilhelm Muller (75, pp. 114-117, Taf. V. Figs. 14, 15) appears to 

 regard the "Testa" of Myxine glutinosa — which I suppose to be the 

 same as the "horny capsule " of Allen Thomson — as resulting from the 

 secretions [metamorphosis 1] of a layer of [granulosa] cells, which imme- 



