Nit-Picking A Post On Hirhurim

Or perhaps not. It is an excellent guest-post by Rav Natan Slifkin about how the gemara could have been aware of nits, yet think lice spontaneously generate, yet call nits "eggs of lice." And it would seem to be true. Check it out there.

However, I think paying attention to the fact that certain segments are stammaic may also be helpful here. Shabbat 107b:

Shabbat 107a:
Mishna: AS FOR THE EIGHT REPTILES [SHERAZIM] WHICH ARE MENTIONED IN THE TORAH, HE WHO CATCHES OR WOUNDS THEM [ON THE SABBATH] IS CULPABLE; BUT [AS FOR] OTHER ABOMINATIONS AND CREEPING THINGS, HE WHO WOUNDS THEM IS EXEMPT; HE WHO CATCHES THEM, BECAUSE HE NEEDS THEM, HE IS LIABLE; IF HE DOES NOT NEED THEM, HE IS EXEMPT, AS FOR A BEAST OR BIRD IN ONE'S PRIVATE DOMAIN, HE WHO CATCHES IT IS EXEMPT; HE WHO WOUNDS IT IS CULPABLE.

107b:
Gemara: BUT OTHER ABOMINATIONS, etc. But if one kills them, he is culpable: which Tanna [holds thus]? Said R. Jeremiah, It is R. Eliezer. For it was taught, R. Eliezer said: He who kills vermin on the Sabbath is as though he killed a camel on the Sabbath. R. Joseph demurred to this: The Rabbis disagree with R. Eliezer only in respect to vermin, which does not multiply and increase, but as for other abominations and creeping things, which multiply and increase, they do not differ [therein]. And both learn it from none but the rams. R. Eliezer holds, It is as the rams: just as there was the taking of life in the case of the rams, so whatever constitutes the taking of life [is a culpable offence]. While the Rabbis argue, It is as the rams: just as rams multiply and increase, so are all which multiply and increase [of account]. Said Abaye to him, Do not vermin multiply and increase? But a Master said: 'The Holy One, blessed be He, sits and sustains [all creatures], from the horns of wild oxen to the eggs of vermin'? — It is a species called 'eggs of vermin'. But it was taught: Tippuyyi and the eggs of vermin? — The species is called 'eggs of vermin'. But there is the flea, which multiplies and increases, yet it was taught, If one catches a flea on the Sabbath: R. Eliezer declares him liable, while R. Joshua exempts [him]? — Said R. Ashi: You oppose catching to killing! R. Eliezer and R. Joshua disagree only in that one Master holds: If the species is not hunted, one is liable; whilst the other Master holds: He is exempt. But in respect to killing even R. Joshua agrees.

ושאר שקצים כו': הא הורגן חייב
מאן תנא א"ר ירמיה ר"א היא דתניא ר"א אומר ההורג כינה בשבת כהורג גמל בשבת
מתקיף לה רב יוסף עד כאן לא פליגי רבנן עליה דרבי אליעזר אלא בכינה דאינה פרה ורבה אבל שאר שקצים ורמשים דפרין ורבין לא פליגי ושניהם לא למדוה אלא מאילים רבי אליעזר סבר כאילים מה אילים שיש בהן נטילת נשמה אף כל שיש בו נטילת נשמה ורבנן סברי כאילים מה אילים דפרין ורבין אף כל דפרה ורבה
א"ל אביי וכינה אין פרה ורבה והאמר מר יושב הקב"ה וזן מקרני ראמים ועד ביצי כינים
מינא הוא דמיקרי ביצי כינים
והתניא טפויי וביצי כינים מינא הוא דמיקרי ביצי כינים
והרי פרעוש דפרה ורבה ותניא הצד פרעוש בשבת רבי אליעזר מחייב ורבי יהושע פוטר
אמר רב אשי צידה אהריגה קרמית עד כאן לא פליגי רבי אליעזר ור' יהושע אלא דמר סבר דבר שאין במינו ניצוד חייב ומר סבר פטור אבל לענין הריגה אפילו רבי יהושע מודה:

I would argue that, as per the usual style, after Abaye's objection, the following give and take is not Rav Yosef and Abaye, but rather simple the setama digmara going systematically through sources. And Rav Yosef might well have not replied this.

If so, Abaye's objection still stands.

Since Rav Ashi appears to explain the dispute in line with Rav Yosef, the setama has to explain how Rav Yosef would respond to this objection. (And would then rely on contemporary scientific sources, such as this opinion of Aristotle about nits.)

Perhaps one can cast Rav Ashi's statement otherwise -- if one claims that his statement was initially shorter, but worked into the discussion. That is, say that Rav Ashi he offers an alternative to Rav Yosef's distinction of spontaneous generation vs. being fruitful and multiplying. Say instead that this dispute of Rabbi Eliezer and the Sages is about whether there tzeida, catching, is common for this species. After all, in the 39 melachot, shechita follows tzeida, and one might read one as a continuation of the other. Thus, Rabbi Eliezer holds they are disjoint and so one can be liable for killing a species which is not caught, while Rabbi Yehoshua, and (perhaps =) the Sages hold that one can only be liable for killing a species which is caught.